9?-O Table of Contents

FISHERY INVESTIGATION OF LAKE MEAD, ARIZONA-NEVADA,

FROM SEPARATION RAPIDS TO BOULDER CANYON, 1978-79

Terry C. McCall

Arizona Game and Fish Department Region III Office Kingman, Arizona 86401

Final Report Contract Number 8-07-30-X0025

U.S. Department of the Interior, Water and Power Resources Service Lower Colorado River Region Boulder City, Nevada 89005 /9?-O TABLE OF CONTENTS

LIST OF TABLES ......

LIST OF FIGURES ......

INTRODUCTION ...... 1 DESCRIPTION OF LAKE MEAD ...... 2 History of the Lake Mead Fishery ...... 5 METHODS AND MATERIALS ...... 9 Aquatic and Riparian Vegetation .... 10 Aquatic Invertebrates .... 10 Zooplankton ...... 10 Zoobenthos ...... 10 Fish ...... 10 RESULTS ...... 12 Aquatic and Riparian Vegetation .... 12 Aquatic Invertebrates ...... 15 Zooplankton...... 15 Zoobenthos ...... 16 Fish ...... 23 Relative abundance .... 23 Disease ...... 43 Life histories ...... 48 native species .... 48 speckled dace, Rhinichthys oscaws (Girard) ...... 48 razorback (humpback) sucker, Xykauchen texanws (Abbott) ...... 52 flannelmouth sucker, Cataotomm tatipirmiz (Baird and Girard) ...... 60 bluehead mountain-sucker, Pantoztews dizcobotu6(Cope) ...... 63 introduced species ...... 66 threadfin shad, Doltozoma petenense (Gunther) ...... 66 rainbow trout, Sam gailtdnoti. ( Richardson) ...... 71. carp, Cypninuz caApio (Linnaeus) ...... 79 red shiner, Notitopis tanens-is (Baird and Girard) ...... 85 fathead minnow, Pimephaes imometaz (Rafinesque) ...... 88 channel catfish, Ictamws punctatws (Rafinesque) ...... 91 yellow bullhead, Ictatultu3 natati6 (Le sueur) ...... 98 black bullhead, letatuAto maws (Rafinesque) ...... 102 Rio Grand killifish,Fundutm zeiminws (Jordan and Gilbert) 104 mosOitofish, Gambu4ia abiiiviz (Baird and Girard) ...... 106 str4ed bass, Monone 4axatiti4 (Walbaum) ...... 111 largemouth bass, Kinoptenws 6atmoide (Lacepede) ...... 122 blutgill, Leponbs macnochi4to ( Rafinesque) ...... 131 green sunfish, ChaenobAyttto cganeftws (Rafinesque) 135 black crappie, Pomoxi4 prigumaCutatuz (Le sueur) ...... 141 green sunfish, ChaenobAuttus cyancteu6 x bluegill, Lepombs manockinas (hybrid) ...... 147 Hypothetical occurrences ...... 148 native species ...... Little Colorado Riverspinedace, Lep-cdomeda vittata ( Cope) .... 148 Virgin River spinedace, Lepidomeda mottioini4 motti4pin,i4 (Miller and Hubbs) ...... 148 Moapa dace, Moapa cotiacea (Hubbs and Miller) ...... 151 woundfin, Reagopteku4 akgenti44imws (Cope) ...... 151 humpback chub, Gita cypha (Miller) ...... 152 bonytail chub, Gita etegan4 (Baird and Girard) ...... 153 roundtail chub, Gita Aobu.sta (Baird and Girard) ...... 154 Colorado River squawfish, PtychocheituA tuciu4 (Girard) ...... 155 Gila mountain-sucker, Panto4teto ctaitki (Baird and Girard) .... 156 flannelmouth sucker, Cato4tomm tatippin,bs x razorback (humpback) sucker, Xytauchen texanws (hybrid) ...... 157

introduced species ...... 158 freshwater eel, Anguitta 0 ...... 158 "walking" catfish, CtaAxiais batAachm (Linnaeus) ...... 158 green swordtail, Xiphophotws hetteni (Heckel) ...... 159 southern platyfish, Xipop1Loku4 macutatws (Gunther) ...... 159 smallmouth bass, Micupteuz dotomieui (Lacepede) ...... 159 walleye, Stizostedion vititeum bitneum (Mitchill) ...... 159 convict cichlid, Cichtazoma nigAo6cociatum (Gunther) ...... 160 banded cichlid, Cichtazoma 6evekum (Heckel) ...... 160 goldfish, Canzoiclis au/Latta (Linnaeus) ...... 160 golden shiner, Notemigonto ciftooteucu6(Mitchill) ...... 160 redside shiner, Richatdzoniws batteatu4 hydrophlox (Cope) ..... 161 leatherside chub, Gita copei (Jordan and Gilbert) ...... 161 Utah chub, Gita atkania (Girard) ...... 162 mountain-sucker, Pantoztews ptatykhynchuis ( Cope) ...... 162 Utah sucker, Catoztomm aulews (Jordan and Gilbert) ...... 162 longjaw mudsucker, Gitticht1iy4 miAab.i.VA (Cooper) ...... 163 mottled sculpin, Cottws baindi ( Girard) ...... 163 brook trout, Savetimus iontinat,i.A (Mitchill) ...... 164 coho (silver) salmon, Oncothynchuz ki6utch (Walbaum) ...... 164 cutthroat trout, Satmo ctakki (Richardson) ...... 165 brown trout, Satmo tkutta (Linnaeus) ...... 165 bowcutt trout, Satmo gaiAdneti (male) x Satmo ctanki (female) 167

LITERATURE CITED ...... 168

11 LIST OF TABLES

Table Page

1 Summary of fish stocking records for Lake Mead, Arizona- Nevada, 1935-1977 ...7

2 List of higher aquatic plants found in Lake Mead, Arizona- Nevada, from Separation Rapids to Boulder Canyon, 1978-1979 ... 13

3 Sampling stations for zooplankton from Separation Rapids to Boulder Canyon in Lake Mead, Arizona-Nevada, 1978-1979 ...... 17

4 Abundance estimates of limnetic zooplankton in Lake Mead, Arizona-NOvada, from Separation Rapids to Boulder Canyon, 1978-1979 ...... 19

5 Sampling stations for benthic invertebrates from Separation Rapids to Boulder Canyon in Lake Mead, Arizona-Nevada, 1978-1979 ...... 21

6 List of benthic invertebrate taxa collected from Lake Mead, Arizona-Nevada, 1977-1978 ...... 22

7 The numbers of benthic invertebrates collected from 26 transects across the littoral zone of Lake Mead from Spencer Creek to Boulder Canyon, Arizona-Nevada, 1978-1979 ...... 24

Abundance estimates of benthic invertebrates in Lake Mead collected from the littoral zone at 26 locations from Separation Rapids to Boulder Canyon, 1977-1978 ...... 31

9 Relative abundance of benthic invertebrate organisms collected from Separation Rapids to Boulder Canyon, Lake Mead, Arizona- Nevada, 1977-1978 ...... 32

10 Sampling stations for fish populations from Separation Rapids to Boulder Canyon in Lake Mead, Arizona-Nevada, 1978-1979 ..... 33

11 Numbers of each fish species collected at 57 sampling locations from Separation Rapids to Boulder Canyon, Lake Mead, Arizona- Nevada, 1978-1979 ...... 36

12 Summary of seine collecting data from Separation Rapids to Boulder Canyon, Lake Mead, Arizona-Nevada, 1978-1979 ...... 39

13 Summary of trammel and gill netting data from Separation Rapids to Boulder Canyon, Lake Mead, Arizona-Nevada, 1978-1979 ...... 40

14 Summary of electroshocking data from Lake Mead, Arizona-Nevada, 1978-1979 ...... 41

15 Relative abundance of 19 fish species collected from Separation Rapids to Boulder Canyon, Lake Mead, Arizona-Nevada, 1978-1979 . 42

111 LIST OF TABLES (Cont.)

Table Page

16 List of fish parasites from Lakes Mead and Mohave (From Roden 1978) ...... 44

17 Parasites of the Lake Mead fishes collected from Separation Rapids to Boulder Canyon, Arizona-Nevada, 1978-1979 ...... 45

18 Summary of observations and collections of razorback suckers in Lake Mead, Arizona-Nevada, 1967-1979 ...... 54

19 Length, weight and condition factor data of Lake Mead fishes collected from Separation Rapids to Boulder Canyon, Lake Mead, Arizona-Nevada, 1978-1979 ...... 55

20 Fecundity estimates of 13 channel catfish from Lake Mead, Arizona-Nevada, 1978-1979 ...... 95

21 Food habits of channel catfish from Lake Mead, Arizona-Nevada.... 97

22 Summary of striped bass stocking records in Lake Mead, Arizona- Nevada ...... 114

23 Stomach contents of striped bass from Lake Mead, Arizona-Nevada.. 119

24 Summary of largemouth bass stocking records for Lake Mead, Arizona-Nevada, 1935-1977 ...... 124

25 Average growth (cm) at scale annuli of largemouth bass in Lake Mead, Arizona-Nevada ...... 127

26 Known hybrids of green sunfish, Chaenob4yttu4 cyaneteu4, and bluegill Leponbs mactochinta ...... 149

i v LIST OF FIGURES

Figure Page

1. Map of Lake Mead, Arizona-Nevada showing the locations of sampling stations for zoobenthos zooplankton tik), and fish OW 1978-1979 ...... 18

2. Estimates of total harvest and percent total catch of rainbow trout from Lake Mead, Arizona-Nevada, 1958-1977 ...... 78

3. Estimates of total harvest and percent total catch of channel catfish from Lake Mead, Arizona-Nevada, 1958-1977 ...... 99

4. Estimated total harvest and total catch of striped bass from Lake Mead, ArizOha-Nevada, 1970-1977 ...... 121

5. Estimates Of total harvest and percent total catch of largemouth bass from Lake Mead, Arizona-Nevada, 1958-1977 ...... 130

6. Estimates of total harvest and percent total catch of bluegill from Lake Mead, Arizona-Nevada, 1958-1977 ...... 137

7. Estimates of total harvest and percent total catch of black crappie from Lake Mead, Arizona-Nevada, 1958-1977 ...... 146

8. Estimates of total harvest and percent total catch of cutthroat trout from Lake Mead, Arizona-Nevada, 1972-1977 ...... 166 1

INTRODUCTION

This investigation of the Lake Mead fishery was conducted by the

Arizona Game and Fish Department for the Water and Power Resources

Service (previously U.S. Bureau of Reclamation) to provide baseline fishery data for inclusion in future environmental impact statements on the lower Colorado River. The area of study was the upper end of the

Lake Mead Recreation Area from Separation Rapids in the Colorado River to

Boulder Canyon.

The study was initiated in June, 1978 with the prime objective of compiling an inventory of fish species present and determining their distribution and relative abundance. Much of the information was gleaned from the records of the Arizona Game and Fish Department and the

Nevada Division of Wildlife (previously Nevada Fish and Game Department).

Additional data was obtained from scientific articles and published reports pertaining to the aquatic ecology of the reservoir. In many cases, where historical information was sparse or nonexistent, field collections were made to compliment existing data in order to ascertain the present status of certain species. The biology of each species collected is discussed including data from field observations and lab analyses where it is sufficient; however, due to the limited time and available manpower, much of the life history information is a collation of more complete and detailed treatments by other authors. 2

DESCRIPTION OF LAKE MEAD

The construction of Hoover Dam across Black Canyon on the Colo- rado River between Arizona and Nevada began in 1931 and was completed in 1935. The newly created reservoir reached capacity in 1941 and was named Lake Mead, in honor of Dr. Elwood Mead, Commissioner of the U.S.

Bureau of Reclamation (USBR) from 1924 to 1936 (USBR Cons. Bul. #9, 1941). The Hoover Dam-Lake Mead project created a multiple purpose reservoir providing flood controls; water for agricultural, municipal and industrial needs; and hydroelectric power. The National Park Ser- vice (NPS) was responsible for planning, developing and administering the recreational resources with the exception of fish and wildlife which were jointly managed by the Arizona Game and Fish Department (AGFD) and the Nevada Division of Wildlife (NDW). Water manipulation through the dam remained in the control of the USBR.

The lake stretches 185 km along an east-west axis forming three major basins (Gregg, Virgin and Boulder) connected by narrow, deep canyons. The Overton Arm extends northward into Nevada from the widest point across the Virgin Basin (2.9 km). At maximum storage, the lake covers 63,902 ha with a volume of 32,937 x 106 m3 and 1,363.8 km of shoreline.

Surface water temperature fluctuates seasonally from about 20 to

29°C. During the summer months, water temperatures in shallow areas may reach over 32°C. Apparently the record high was in August, 1952 when Jonez and Sumner (1954) recorded a water temperature of 34.1°C. The lake begins to thermally stratify in late May or June with a a distinct 3 thermocline forming at a depth of 10-15 m by July (Moffett 1943, Howard

1954). The thermal gradient begins at a depth of about 3 m then grad- ually extends to about 10 m as the reservoir warms. A fall turnover begins in October when the thermocline sinks and eventually disappears at a depth of 40 m. By January or early February the monomictic lake is completely destratified (Jonez and Sumner 1954, Deacon 1976). Dis- solved oxygen is abundant throughout the water column during the winter months with at least 4 ppm of oxygen in the hypolimnion (Jonez and Sumner

1954). A negAtive heterograde oxygen profile is formed during the period of stratification due to biological respiration at the metalimnion.

The water in Lake Mead is generally clear allowing light to pene- trate quite deep in the water column; secchi disc readings in excess of

13 m were frequently recorded throughout the year. As would be expected, water is more turbid in areas where the three major tributaries enter the reservoir. Water transparency is reduced to 10-13 cm near the mouths of the Virgin and Moapa Rivers in the Overton Arm and below the silt-laden Colorado River in the upper end of the lake. Clarity grad- ually improves from the God's Pocket area to the entrance of Grand Wash as the cold Colorado River slowly flows along the bottom of the reservoir.

The irregular shoreline of the lake is both volcanic and sedimen- tary in origin. Sheer cliffs rise above narrow twisting inlets and fingers, supporting a variety of desert shrubs and cacti exemplary of the lower Sonoran life zone. Although the diversity of vegetative types changes from one region to another, the most abundant appears to be 4

Lakua spp. Riparian and aquatic plants are rare. The most common vegetation type immediately adjacent to the shoreline is salt cedar, or

"Tamarisk" (Tamakix pentandka). Sago pondweed, Potamogeton pectinatuz, is the dominant aquatic macrophyte. The distribution and abundance of submersed aquatic plants varies from year to year according to the sever- ity of the seasonal fluctuation in water levels.

There is a marked seasonal rise and fall of the water level which is partially due to the release of reservoir water from March through

November for downstream irrigation. A less obvious fluctuation occurs daily in response to the electrical demand. The loss of water for agricultural and electrical needs is compounded by an estimated 7,402 x 6 3 10 m of water forfeited annually to evaporation (USBR Cons. Bul. #9,

1941).

Shoreline erosion of most of the lake is obvious, especially in the

Overton Arm where deposits of soluble minerals are eroding at an aston- ishing rate. Approximately 18 million metric tons of material were dissolved into the Lake Mead reservoir bed and banks over the period from 1936 to 1948. Of this total, 11 million metric tons were sodium, potassium and chloride (Gould 1954a, 1954b; Howard 1954; Frey 1966). An excellent example of wave cut erosion, resulting in massive shoreline deterioration, is the "Temple" located on the opposite shore across from

Temple Bar Marina in Temple Basin. The altered physiography of the shore and filling of the basin is best demonstrated by Gould (1954) who compared two photographs of the Temple; one taken in 1934 and the other in 1948 (Gould 1954). These photographs show noticeable erosion at the base of the stl"ucture which has contributed to a continual shrinking of the landmark. Maximum depth of the reservoir was over 150 m shortly 5

after it filled, but silt deposition from the Colorado, Moapa and Virgin

Rivers, and shoreline erosion has considerably reduced the mean depth in

the past 45 years.

The lake is classified limnologically, between mesotrophic and oligotrophic throughout. One exception is Las Vegas Bay and Las Vegas

Wash in Boulder Basin, where large quantities of nutrients are discharged from waste water treatment plants. As a result, Las Vegas Bay and Las

Vegas Wash are classified meso-eutrophic and eutrophic, respectively.

The influence of waste water effluent and nutrient loading of Lake Mead is discussed by Hoffman et al. (1970), Deacon (1971), Hoffman (1971), and U. S. Environmental Protection Agency (USEPA) (1971), and the physical limnology of the lake is discussed by Bell (1942), Anderson et al.

(1950), Gould (1951), and Anderson and Pritchard (1951), with particular emphasis on heat budgets and flow patterns.

HISTORY OF THE LAKE MEAD FISHERY

Following the construction of Hoover Dam in 1935, one of the most turbid rivers in the United States was transformed into a clear, deep reservoir suitable for both warm and cold water gamefish but intolerable to most of the native fishes. Although there is no creel information from this area before the closure of Hoover Dam, the Colorado River probably offered only limited recreational use largely because of its inaccessibility. Apparently, a few avid anglers were able to take channel catfish, lc-tau/Luz punctatu6, and the native squawfish or "white salmon", Ptychocheitca tuciu4, which historically were a staple for Indians living near the river.

As the reservoir filled, the rising water inundated trees and 6 shrubs, which provided suitable habitat and foraging areas for centrarchid fishes. From 1935 to 1969 Lake Mead was developed and managed as a warm water fishery with introductions of largemouth bass, Mictoptenus samoides; black crappie, Pommis nignomacutatuz; and bluegill, Leponis mactochaus. A summary of the fish stocking records from 1935 to 1977 is shown on Table 1.

Angler success was greatest during the early years of the reservoir especially along the shallow waters covering abandoned orchards and hedge rows. Crappie and bluegill were abundant and contributed significantly to anglers' creels, while providing an abundant food source for tilt! bass. The 1941 spawning •season was a phenomenal success for centrarchids and the growth rate of largemouth bass was excellent.

As larger bass were caught, the reputation of Lake Mead as a trophy largemouth bass fishery spread nationwide, with promotional help from angling clubs and coverage in sports magazines. When a record largemouth bass (6.01 kg) was taken from Lake Mead in 1939, anglers from throughout the U. S. came to fish the newest largemouth bass "hot spot"-

To provide a forage fish for the largemouth bass, threadfin shad,

Donosoma petenense, were experimentally released in 1954, through a cooperative agreement among Arizona, Nevada, and California. They established quickly and were widespread throughout the reservoir by 1956.

The bass population continued to grow, taking advantage of the prolific threadfin shad. Approximately 400,000 largemouth bass were caught annually from 1935 to 1969 which comprised over 50 percent of the total harvest.

The Lake Mead fishery began to atrophy following the construction Table 1. Summary of fish stocking records for Lake Mead, Arizona-Nevada, 1935-1977.

rainbow cutthroat trout cutthroat trout bowcutt largemouth green threadfin striped coho Year trout strawberry strain) (Lahontan strain) trout bass sunfish shad bass salmon

1935-193.9. - 480,625 - -

1939-1942 - - 286,090 350,145 - - -

1954 - - - - 274 - -

1955 - - - - - 11,000

1964 - 200,000 - - -

1969 80,177 - - - - 20,000 36,710

1970 153,823 - - - - - 41,300 56,116

1971 150,696 - - 910 64,335

1972 180,486 39,988 19,650 - - - 3,000 169,000

1973 172,477 ------

1974 254,240 - - - -

1975 801,861 7,732 28,908 13,343

1976 650,395 120,373 - 11,306 - - -

1977 144,321 - 148,426 10,016 - - 8 of Glen Canyon Dam on the Colorado River above Lake Mead in 1964. An eventual decline in the fishery was anticipated by biologists familiar with the natural evolution of hydroelectric impoundments, but the situation was compounded by a substantial reduction of water volume into Lake

Mead while Lake Powel filled in the late 1960's. Since then, the bass fishery has continued to deteriorate to the point that in 1977 fewer largemouth bass were caught than channel catfish or black crappie.

In 1969, the NDW initiated a five year research project funded by a contribution from the Clark County Convention Authority and matching federal aid (Dingel-Johnson funds) to improve the fishery by diversi- fying the available gamefish species. This program involved the introduction of two exotic salmonids, rainbow trout, Santo gaitdneki, and coho salmon, Oncokhynchws kautch. Other cold-water fish (bowcutt and two strains of cutthroat trout) were released later, but one of these species attained great success.

The most critical, and in my opinion beneficial, change in the fishery was launched in 1969 with the release of 20,000 fingerling striped bass. An edaceous predator, they exploited the numerous shad, grew rapidly and successfully reproduced in 1973. As the anglers learned their habits and became familiar with the fishing gear and methods necessary to catch a fish that preferred the open-water areas, angling effort for the striper grew from only 2.3 percent in 1975 to 11.3 percent in 1977 (MEG 1975, 1976, 1977). The estimated number of stripers taken by anglers jumped from only 185 in 1971 to 13,250 in 1977 and 9

striped bass fishing tournaments and derbies became popular. The fame

and respect the striper is acquiring is in many ways not unlike that

enjoyed by the largemouth bass during its hayday in the 1940's and

1950's.

More detailed information on the status of Lake Mead fishes, their

distribution, life history and present significance to the Lake Mead

fishery is discussed in the results section (pages 12-167).

METHODS AND MATERIALS

AQUATIC AND RIPARIAN VEGETATION

Submersed thacrophytes were collected from 109 bottom samples taken along 26 transects through the study area. Additional collections were made and observations were recorded while conducting routine field activities. Plants were pressed in the field with a standard plant press (40 x 60 cm), the location and general habitat was recorded, and the specimens were returned to the laboratory for identification. Major taxonomic references used to identify aquatic plants include: Kearney and Peebles (1960), Mason (1969), McDougall (1973), Correll and Correll

(1975) and Lehr (1978).

AQUATIC INVERTEBRATES

Zooplankton

The limnetic zooplankton community was sampled at 29 locations along the main axis of the lake from Separation Rapids in the Colorado River to Little Bitter Wash in upper Overton Arm. Samples were taken over a 7- week period from 9 September to 27 October 1978. Plankton were collected 10 with a Wisconsin Plankton Net (80 um mesh) towed horizontally and vertically for 20 m. In order to standardize plankton samples in the

Colorado River where vertical sampling was not possible, the rate of water flow was estimated and the net was then submerged approximately

3 cm below the surface until an equivalent volume of water had been filtered. All plankton samples were preserved in AFA (alcohol, formalin, acetic acid) and returned to the laboratory for analyses. Identifica- tion and enumeration of zooplankton were made with the use of a Sedge- wich-Rafter counting chamber.

Zoobenthos

The benthic invertebrate population was sampled at 26 transects from Surprise Canyon in the Colorado River to Little Bitter Wash in

Overton Arm. Samples were collected over an 8-month period from 26 September

1978 to 23 May 1979. Bottom samples were taken with an Eckman Dredge along transects perpendicular to the shoreline at distances of 1, 3, 5, 10 and

20 m. The substrate size and the type(s) of vegetation were recorded for each sample. Bottom samples were washed through a 600 um standard testing sieve, preserved in AFA, and returned to the laboratory where the benthic fauna were separated from the bottom debris using the salt flotation technique. Organisms were identified and quantified as the number of organisms per square meter of substrate. Major taxonomic references used for insect identification included Pennak (1953) and

Borrow and Delong (1971).

FISH

Lake Mead fish populations were sampled at 57 locations, with trammel and gill nets, seines and an electrofishing unit. Seventy-six collections were made over a 10-month period from 15 July 1978 to 4 April 1979. Trammel nets 11 were 100 m long with 35.6 cm outside wall and 7.6 cm inside mesh.

Experimental gill nets measured 21.3 x 1.8 m with four panels of 2.5,

3.8, 5.0 and 6.4 cm mesh. In mid-lake, two nylon trammel nets and two experimental green gill nets were set at each sampling station. Nets were set perpendicular to the shore; about 1 m below surface and along the bottom. In deep water, a sonar recording device was occasionally used to find concentrations of fish prior to setting the net. A nylon seine (1.0 x 6.1 m - 3.0 mm mesh) was used to sample selected shallow areas suited for seine collecting. Seining data were expressed as the 2 number of each species per area sampled (m ), and netting data (24-hour set) expressed as the number of fish/net/hour for each species. Fish were collected from coves in Gregg and Temple Basins with an electrofishing unit mounted on a barge. A portable electroshocking unit mounted on a rubber Havasu raft was used to sample the mainstream Colorado River below

Separation Rapids. The actual shocking time (i.e. time electrodes are activated) was recorded for all electrofishing activity and the data were expressed as the number of each species collected per minute of shocking time. Electroshocking activities in the Colorado River above

Pierce Ferry were accomplished with equipment and assistance of personnel from the Museum of Northern Arizona (MNA).

Fish were weighed, measured and examined for ectoparasites. Length and weight data were used to calculate coefficient of condition (KTL) 5 3 with the formula K = W x 10 /L (W = total weight in grams and L = total length in mm). Ten specimens of each species per sampling location were sacrificed and examined for endoparasites. Stomach contents were identified and the frequency of occurrence for each major food item was 12 computed. General gonadal condition was noted and ovaries from gravid females were removed and weighed. Scales or spines were taken from a size series of each game fish species to estimate age and evaluate growth.

RESULTS

AQUATIC AND RIPARIAN PLANTS

Ten species of aquatic plants were identified from Lake Mead National

Recreation Area (Table 2). Stands of sedges, Junc116 tonuyi and SciAlows acustas, and cattails, Typha domirgmsi4 and T. anguoti6oZia, were common above Pierce Ferry at the edge of backwaters and abundant at the confluence of Spencer Creek and above the mouth of Surprise Canyon.

Cattails were also established along the margins of dense growths of salt cedar which is dominant along semi-permanent sand bars adjacent to the mainstream Colorado River. Below Pierce Ferry, salt cedar becomes less common along the shores of the reservoir, usually in stands of only

5-10 trees.

Willows,SaLix exigua,were common in Spencer and Surprise Canyons and rare along the shore of the main river down to Emory Falls Canyon.

Generally, where willows and salt cedar grew together along the river bank, the willows were above the zone of waterlevel fluctuations, suggesting they are more susceptible to the vagaries of the rising and falling water level than the salt cedar. In the reservoir, willows are confined to areas in and adjacent to seeps and springs.

Reedgrass, Phnagrai.teis awstnaCL, abundantly grows on the sandy 13

Table 2. List of higher aquatic plants found in Lake Mead, Arizona-Nevada, from Separation Rapids to Boulder Canyon, 1978-1979.

Sago pondweed, Potamogeton pectinatta L.

Holly-leaved water nymph, Najaz matina L.

Horned pondweed, Zannichettia patustALs L.

Horsetail, Equaetum sp.

Common reed, Phtagmite4 auztAatiz (Cav.) Trin.

Narrow-leaved cattail, Typha angtatiOtia L.

Southern cattail, T. domingenza Pers.

Hardstem bulrush, SciApuis acutws Muhl Bulrush, Sahpu4 sp.

Rush, Juncws to44eyi Cav. 14

banks of the Colorado River, but was not collected below Emory Falls

Canyon. A single horsetail, Equi4etum sp., was taken from a backwater area along the Colorado River below the bat caves in the summer of 1978.

This plant probably drifted from the upper reaches of the river in the

Grand Canyon where it is common.

Submersed plants are rare along the shore of the reservoir. Sego pondweed, Potamogeton pectinatuz, is the most prevalent higher aquatic plant found throughout the study area below Pierce Ferry. Typically, pondweed is established to a depth of 10-13 m, depending on the batho- metrics of the shore, and often grows with spiny naiad, Naja matina, and grasswack, ZanichaZia patu/stAZs. Sedges grow sporadically throughout the lake, particularly abundant at the ends of narrow protected fingers. Stands were relatively small, rarely covering more than 1 2 or 2 m .

Where the inclination of the shore is moderate or relatively steep, the water level often drops below the lower limit of the euphotic zone.

In these areas, there is no perennial growth of higher aquatic plants.

In 1952, the following observation was made during an aquatic survey of

Lake Mead:

...aquatic vegetation is conspicuous by its absence. The annual fluctuations of the reservoir are normally too great to ever be compatible to lend themselves to the production of aquatic vegetation (Wagner 1954).

Today there is still an obvious absence of submersed aquatic vegetation in the reservoir. This phenomenon is not unique to Lake Mead, but typical of "bath-tub ring" reservoirs that are drawn down regularly to produce hydropower. 15

Littoral vegetative growth and associated epiphytic algae normally attract and harbor a variety of invertebrates. These organisms, especially the insect larvae, provide an important trophic level for small fish and obligate planktivores (Berg 1950, McGahn 1952). In addition, algae and submersed higher plants directly provide a food supplement for omnivorous game fishes such as ictalurids and smaller centrarchids. The virtual absence of aquatic plants and the associated aquatic invertebrate community eliminates a trophic compartment that is critical to many species that depend on a transitional group of food items as they shift to a piscivorous diet. Additionally, the scarcity of aquatic plants that ordinarily provide escape cover and concealment for young fish could only enhance predation and abate successful recruitment.

AQUATIC INVERTEBRATES

Zooplankton

Zooplankton populations in Lake Mead have been described as rich and diverse but unevenly distributed (Dwyer 1951). Typically, plankton are distributed from 2.4 to 6.1 m below thesurface on bright days and closer to the surface (1.2 to 3.0 m) on cloudy days. A later investigation on the vertical distribution of plankton reported viable populations (0.2 to 1.0 cc per standard haul) in the upper 4.6 m during sunny days and as deep as 12.2 m on overcast days (Dwyer 1952). NDW found moderate numbers of plankton (0.4 to 0.8 cc per 1 min. haul) that increased during periods of high water with volumes ranging from .6 to

2.2 cc per 7.3 m vertical tow (Jonez and Sumner 1954). The limnetic zooplankton community in Boulder Basin has been examined in relation to 16 the cyclic reduction in metalimnetic oxygen with results indicating the zooplankters are responsible for a significant portion of the oxygen depletion. With the metalimnion divided into two 15 m layers, the zooplankton consumed 33 to 69 percent of the daily oxygen from the upper section and 12 to 42 percent from the lower section (Burke 1977).

The limnetic zooplankton community was sampled at 29 locations during 1978 and the spring of 1979. The names of sampling sites are listed on Table 3 and the locations are shown on Figure 1. Total abundance estimates for each location ranged from 0 orgs/1 in the mainstream

Colorado River to 89.4 orgs/1 in lower Overton Arm (Table 4). The average was 37.4 orgs/1. Organisms were quantified into three major taxa:

Cladocera, Copepoda and Rotifera. The cladocerans were the dominant group (18.4 orgs/1) followed by copepods (12.6 orgs/1) and rotifers

(6.4 orgs/1) (Table 4). The data suggest the most productive area' of the lake is Overton Arm (62.3 orgs/1) followed by Temple Basin (46.9 orgs/1), Virgin Basin (42.2 orgs/1), Grand Wash (38.1 orgs/1), and Gregg

Basin (34.6 orgs/1). This information was collected throughout the year and does not consider seasonal variations in abundance of species composition.

Zoobenthos

Moffett (1943) found the production of bottom organisms in Lake

Mead to be very poor when he examined twelve bottom samples and found only one midge larva. Samples were taken at depths ranging from 6.1 to

32.6 m in Detrital Wash and Temple Bar and washed through a 600 um screen. Similar results were obtained by Jonez and Sumner (1954) when they reported the normal insect population of Lake Mead is "very meager". 17 Table 3. Sampling stations for zooplankton from Separation Rapids to Boulder Canyon in Lake Mead, Arizona -Nevada,1978-1979.

Station Station Station Number Name * Location

1 Separation Rapids - 2 Spencer Creek IT 3 Surprise Canyon 0> 4 Bat Cave 1-". •R-• " 0 CE 5 "The Sink _____

' 6 God s Pocket " 7 "Antsgalore Cove 8 " Gill Net Station" j 0 _0 9 Lava Point m (1) 10 s. m Bradley Bay c..u, 11 South Howland Cove __

12 South Cove 13 Sandy Point 14 Sunfish Cove 15 Wagon Trail Bay 010 CI) V) 16 Trail Rapids Bay S., m 17 Slide Cove c..vi co 18 Hualapai Isle _I_

19 The Temple ---J-- R— C 20 Haystacks 0„ E (A 21 The Jawbone CU cu 3 2:31.

22 Secret Cove -7— 23 Boulder Point CH •,- S- V) 24 Middle Point .R. nj

' 25 Miner s Cove -7— 26 Jim Jones Reef 0 27 Meat Hole t!cu.< E 28 Salt Cove > 29 Little Bitter Wash

* Collecting sites are identified from the National Park Service Lake Mead National Recreation Area Cove Name Map. The locations of areas previously unnamed (in quotes) are shown in Figure I. •

LAKE MEAD, ARIZONA-NEVADA SEPARATION RAPIDS TO BOULDER CANYON

FIGURE 1 09,19r too o•oca MAP OF LAKE MEAD, ARIZONA - NEVADA, SHOWING THE LOCATIONS of SAMPLING STATIONS FOR ZOOBENTHOS ( 0), ZOOPLANKTON (*), AND FISH (0) 1978 - 1979.

Echo Day

7 &rood •osio 14. ichbeto Con Ton ecueso , Corn",

Porch Pj F•rry41 11 t S C0 _ LAKE MEAD -1 A.7..“, co. 0. x.4 .1 041 7 I -"....e..- 4 1 3 30 NATIONAL 31 I5 " T•ople Do -53 1.1 I LAKE MEAD ▪ v Ccw.).cri.‘ g RECREATION AREA NATIONAL ii r RECREATION AREA r-1

SCALE I: 500,000 1. 3 100113111 MLIALAPAI 0 10 KM INDIAN 1 R. d$ RES E RN.ZTION 19

Table 4 . Abundance estimates of limnetic zooplankton in Lake Mead, from Separation Rapids to Boulder Canyon, Arizona-Nevada, 1978-1979. Values are expressed as organisms per liter.

Sampling orgs/L station Cladocera Copepoda Rotifera Total

1 4.5 0 0 4.5 2 4.9 4.9 2.5 12.3 3 0 0 0 0 4 2.3 0 0 2.3 5 8.3 0.3 8.3 16.9 6 5.1 0 0 5.1 7 22.8 2.5 0 25.3 8 19.7 27.1 2.4 49.2 9 33.4 9.5 23.8 66.7 10 4.6 2.3 2.3 9.2 11 21.8 14.6 36.4 72.8 12 2.5 14.8 2.6 19.7 13 4.7 4.7 2.4 11.8 14 14.9 17.4 17.4 49.7 15 22.3 17.4 5.0 44.7 16 23.5 7.1 2.3 32.9 17 16.5 16.5 2.4 35.4 18 17.0 31.5 0 48.5 19 21.9 4.9 4.9 31.7 20 24.3 19.6 0 43.9 21 24.2 33.8 7.2 65.2 22 12.4 2.5 2.5 17.4 23 14.2 9.5 7.0 30.7 24 54.6 4.8 19.0 78.4 25 49.7 39.7 0 89.4 26 28.3 18.9 14.1 61.3 27 29.0 6.5 6.4 41.9 28 27.8 27.8 13.8 69.4 29 19.8 27.2 2.5 49.5 20

The most abundant group was the midges (Tendipedids) which were found in the greatest numbers during the summer months. Other invertebrate taxa included damselflies, dragonflies, water boatmen, backswimmers and several species of "flies". Although the majority of studies have found very few benthic invertebrates, there is one conflicting report stating both plankton and bottom samples as rich, but unevenly distributed (Dwyer

1952). Dwyer found "numerous" bloodworms and other midge larvae in mud bottoms at depths of 7.6 to 30.5 m.

Analysis of bottom samples from 26 littoral transects (Table 5,

Figure 1) in 1978-79 revealed 13 species of bottom invertebrates (Table 6).

Only two specimens of the Asiatic clam, Ccothicuta manitemiz, were encountered during 1977-78; one collected from a bottom sample taken at a depth of 9.4 m in Teakettle Bay (Virgin Basin) and the other was found floating at the surface in Overton Arm, Scuds, GammaAws tacu4tA,b6, are a major dietary component of most fishes within the Grand Canyon and support the salmonid fishery above Lake Mead (Stone 1964, 1965a,

1965b, 1967, 1968, 1969, 1971, 1972; Bancroft and Sylvester 1978, 1979).

Scuds were absent from bottom samples taken in the river, but were found clinging to drifting algae that became entangled in trammel nets. They apparently do not inhabit the reservoir since they were not found in dredge samples or fish stomachs.

It is interesting that earlier studies of the fishery in the 1940's and 1950's cite local reports of crayfish along the shore but apparently they were not collected or observed during the course of these investigations (Moffett 1943, Jonez and Sumner 1954). Jonez and Sumner (1954) stated that there was little evidence to indicate any form of crayfish was 21

Table 5. Sampling stations for benthic invertebrates from Separation Rapids to Boulder Canyon in Lake Mead, Arizona-Nevada, 1978- 1979.

Station Station Station Number Name * Location

1 Spencer Creek 2 Surprise Canyon 3 Tincanebitts Canyon if,s- w 0 > 4 Bat Cave 5 "Green Rock Backwater" e., er

6 South Cove 7 Wagon Trail Bay 0), 8 Granite Cove w 0m 9 Spring Cove 10 Hualapai Bay 11_7 11 Gateway Cove 12 Temple Bar 71- 13 Trail Rapids Bay 1 14 Haystack Bay 4.3E n3u) 15 Campanile 16 Grebe Bay 2 17 Teakettle Bay 18 Little Gyp Beds ...- ---c-01,-T 19 "Broken Oar Bay" s- 0 20 "Walker Bay Backwater" 21 Walker Bay f---T-. 22 Miner's Cove 23 Tim Jones Reef —: 0 1-- 24 Cottonwood Cove t E 25 Salt Bay > 26 Little Bitter Wash :7

* Collecting site names are taken from the National Park Service Lake Mead National Recreation Area Cove Name Map. The locations of previously unnamed areas (in quotes) are shown on Figure X. 22

Table 6. List of benthic invertebrate taxa collected from Lake Mead, Arizona-Nevada, 1977-1978

Insecta

Plecoptera NemouAidae

Odonata Libettadae Coenaytinonidae

Hemiptera Gervadae Beto4tomatidae Notonectidae

Tricoptera

Col eoptera Dystiscidae

Diptera Simaiidae Chitonomidae

Gastropoda Physa sp.

Pelecypoda Cotbicaa manitens,bs

Decapoda Pnocambartaz ceank.U.

Annelida

01 i gochaeta Tubi6ia.dae 23

established, other than perhaps temporarily, in the lake. Recent evi-

dence suggests that crayfish, Pucambau4 aatki, are well established

and are important to the fishery as a dietary component of largemouth

bass, striped bass and channel catfish, at least during the summer

months (see Food Habits sections). Crayfish were observed while

electrofishing and snorkeling in the Gregg and Temple basins and are

presumed to occur throughout the lake.

Abundance of bottom invertebrates at each transect ranged from zero

to 0.763 orgs/m2 (Tables 7 and 8). The most common invertebrate was the

midge (14.3% freq. occur.) followed by tubificid oligochaetes (7.1%

freq. occur.) (Table 9). Generally, these results support those of

earlier studies which indicate an extremely depauperate benthic inver-

tebrate population. The relatively few numbers of bottom invertebrates, especially aquatic insect larvae, as compared to more "stable" reser-

voirs is directly related to the annual fluctuation of the water level.

The constant exposure of the upper littoral zone reduces the amount of suitable habitat by precluding the establishment of perennial aquatic plants and the invertebrate fauna that is normally associated with submersed plants.

FISH

Relative Abundance

Fish were collected with gill and trammel nets, seines and electrofishing gear from July, 1978 through April, 1979. A total of 10,129 fish representing 19 species was collected from the 57 sampling sites.

(Table 10, Figure 1). The numbers of each species taken at each location Table 7. The numbers of benthic invertebrates collected from 26 transects across the littoral zone of Lake Mead from Spencer Creek to Boulder Canyon, Arizona-Nevada, 1978-1979. ND = No Data

Sampling Stations

Distance 1 2 3 Sample from Spencer Canyon Surprise Canyon Tincanebitts Canyon No. shore(m) taxon orgs/m2 taxon orgs/m2 taxon orgs/m2 I 1 Simuliidae 0.465 Simuliidae 1.265 - 0 Nemouridae 0.047 Chironomide 0.326 Tricoptera * ND

II 3 - 0 Simuliidae 0.674 - 0 Dytiscidae 0.023

' III 5 Simuliidae 0.256 - 0 - 0

IV 10 ND ND ND ND ND ND

V 20 ND ND ND ND ND ND i

* Unidentified fragmented cases Table 7. (continued)

Sampling Stations 4 5 6 Sample Bat Cave "Greenrock Backwater" South Cove No. taxon orgs/m2 taxon orgstm2 taxon orgs/M2

I Libelludae 0.023 Physa sp. 0.14 - 0 Chironomidae 0.326

II - 0 Physa sp. 0.465 _ _ Chironomidae 0.047

III - 0 Physa sp. 0.093 Chironomidae 0.14 Chironomidae 0.093

IV ND ND Chironomidae 0.209 - 0

V ND ND Physa sp. 0.07 - 0 Table 7. (continued)

Sampling Stations 7 8 9 Sample Wagontrail Bay , Granite Cove Spring Cove , 4 No. taxon orgs/m4 taxon orgs/m2 taxon orgs/m , I - 0 - 0 Belostomatidae 0.023 Gerridae 0.512 Chironomidae 0.721 II - 0 Libelludae 0.14 _ Chironomidae 0.721 0

III Chironomidae 0.07 _ 0 Chironomidae 0.07

IV - 0 _ 0 - 0

V _ 0 _ 0 _ 0 Table 7. (continued)

Sampling Stations 10 11 12 Hualapai Bay Gateway Cove Temple Bay Sample 2 No. taxon orgs/m2 taxon orgs/m2 taxon orgs/m

I - 0 - 0 - 0

II - 0 - 0 - 0

III - 0 - 0 Tubificidae 0.14

IV ND ND Tubificidae 0.093 ND ND

V ND ND Tubificidae 0.395 ND ND

Sampling Stations 13 14 15 Trailrapids Bay Haystack Bay Campanile Sample 2 2 No. taxon orqs/m taxon orgs/m taxon orgs/m2

I - 0 - 0 - 0

II Physa sp. 0.047 - 0 - 0

III - 0 - 0 - 0

IV ND ND - 0 Tubificidae 0.047

V ND ND 0 - 0 Table 7. (Continued)

Sampling Stations Sample 1 6 la Greb'e Bay TeakRtle Little b yp Beds , No. , Bay 1 taxon orgs/e taxon orgs/m" taxon orgshe

I - 0 - 0 - 0

II - 0 Chironomidae 0.233 Chironomidae 0.07 Physa sp. 0.279 III - 0 Physa sp. 0.093 Chironomidae 0.233 Tubificidae 0.209 . IV - 0 Corbiculidae 0.023 - 0 Cmbicuta maniZensis

V - 0 - 0 - 0 Table 7. (continued)

Sampling Stations 19 20 21 Sample "Broken Oar Bay" , "Walker Bay Backwater" Walker Bay No. taxon orgs/m' taxon orgs/m2 taxon orgs/m2

I Chironomidae 0.79 Gerridae 0.349 - 0 ChironomidaP 0.558 Elmidae 0.023 Notonectidae 0.07

II - 0 Gerridae 0.093 - 0 Chironomidae 0.372 Coenagrionidae 0.047

III - 0 - 0 Tubificidae 0.163

IV _ 0 - 0 Tubificidae 0.093

V - 0 - 0 - 0 Table 7. (continued)

Sampling Stations 22 23 24 25 26 Sample Miner's Cove Jim Jones Reef Cottonwood Cove Salt Bay Little Bitter Wash 2 No. 2 taxon orgs/m taxon orgs/m2 taxon orgs/m2 taxon orgs/m2 taxon orgs/m

I - 0 - 0 - 0 - 0

II - 0 Chironomidae 0.186 - 0 - 0 - 0

III - 0 Chironomidae 0.093 - 0 - 0 - 0

IV - 0 - 0 - 0 - 0 Tubificidae 0.07

V - 0 Chironomidae 0.186 Tubificidae 0.163 - 0 - 0 - 0 31

Table 8. Abundance estimates of benthic invertebrates in Lake Mead collected from the littoral zone at 26 locations from Separation Rapids to Boulder Canyon, 1977-1978.

Station Number of Number of 2 Number samples invertebrate taxa orgs/m

1 6 3 0.256 2 6 3 0.763 3 6 0 0 4 6 1 0.008 5 10 2 0.289 6 10 1 0.03 7 10 1 0.014 8 10 2 0.172 9 10 3 0.265 10 6 0 0 11 10 1 0.098 12 6 1 0.045 13 6 1 0.016 14 10 0 0 15 10 1 0.016 16 10 0 0 17 10 3 0.126 18 10 2 0.102 19 10 1 0.158 20 10 5 0.3 21 10 1 0.051 22 10 0 0 23 10 2 0.112 24 10 0 0 25 10 0 0 26 10 1 0.014 32

Table 9. Relative abundance of benthic invertebrate organisms collected from Separation Rapids to Boulder Canyon, Lake Mead, Arizona- Nevada, 1977-1978.

Percent 2 taxa frequency of occurrence orgs/m

Chironomidae 14.3 0.281 Tubificidae 7.1 0.153 Phy4a sp. 6.3 0.178 Simuliidae 3.1 0.665 Gerridae 2.4 0.318 Libelludae 1.6 0.082 Tricoptera 0.8 - Gerridae 0.8 0.512 Notonectidae 0.8 0.07 Coenagrinonidae 0.8 0.047 Nemouridae 0.8 0.042 Cokbicutua manitenzis 0.8 0.023 Dytiscidae 0.8 0.023 Elmidae 0.8 0.023 Belostomatidae 0.8 0.023 33 Table 10. Sampling stations for fish populations from Separation Rapids to Boulder Canyon in Lake Mead, Arizona-Nevada, 1978-1979.

Station Station Station Number Name * Location

1 River Mile 241.5 2 River Mile 242 3 River Mile 243 4 River Mile 244.4 5 River Mile 246 (Spencer Canyon) 6 River Mile 248.5 (Surprise Canyon) 7 River Mile 263.7 (Tincanebitts Canyon) 8 River Mile 266.5 (Bat Cave) 9 River Mile 267.5 "The Sink" 10 River Mile 269 "Green Rock Backwater" 11 River Mile 269.9 "Dead Cormorant Backwater" 12 River Mile 273.1 "Sheep Backwater" 13 River Mile 274.4 (Emory Falls Canyon)

14 "Lower Pierce Ferry" 15 God's Pocket 16 "Gill Net Cove" 17 "Antsgalor Cove" 18 Lava Point

19 Bradley Bay 20 North Howland Cove 21 Sunfish Cove 22 Crappie Cove 23 North Bay 24 South Bay 25 "South Cove #1" 26 "South Cove #2" 27 "South Cove #3" 28 Wagon Trail Bay 29 "Carp Cove" 30 Lower Smith Bay 31 "Cove #18" 32 Upper Hualapai Bay 33 Lower Hualapai Bay

34 Granite Cove 35 Spring Cove 36 Burro Bay 37 Wild Burro Bay 38 Heron Point 39 Trail Rapids Bay 40 "Burton's Finger #1" 41 "Burton's Finner #2" 42 Lower Haystaa Bay 34 Table 10 (continued)

Station Station Station Number Name * Location

43 Catclaw Cove 44 Jim Jones Reef I 45 Ebony Island 46 Meat Hole ‹ce 47 "Motherbear Bay" c .i.w, 48 Salt Cove s_ w 49 Little Bitter Wash > 50 Mouth of Virgin River cl 51 Mouth of Muddy River

52 "Broken Oar Bay" 53 West Gypsum Bay ...-szi c 54 Danger Bay 55 Pool Islands ...- m 56 Stewart Cliffs ›. co 57 Boulder Wash

* Location names are taken from National Park Service Lake Mead National Recreation Area Cove Name Map (3rd printing) and the Grand Canyon River Guide. The locations of collecting sites previously unnamed (in quotes) are shown in Figure 1. 35

are shown on Table 11. Sampling methods used at each of the stations

were dependent on the physiography of the area and weather conditions.

Seine sampling at 16 locations yielded 9,404 fish representing

13 species. The total area sampled was 6,423 m2. Three species com-

prised 90 percent of the fish from all seine collections: red shiners

Rhiniehthyes (meatus; threadfin shad and mosquitofish, Gambu4ia a60142.

Red shiners were collected abundantly (0.63 fish/m2) in the Colorado

River and near the mouths of the Virgin and Moapa Rivers, but were

only taken at one location in the main reservoir. Threadfin shad were

collected sporadically throughout the lake (0.5 fish/m2) and were most

heavily concentrated near the mouth of the Virgin River. Mosquitofish 2 were also most numerous in the warm water tributaries (0.21 fish/m )

and below seeps that drain into the reservoir. The numbers of each

species taken from seine collections is shown on Table 12.

Gill and/or trammel nets were fished for 24 hours at each of 25

stations for a total of 600 net-hours. A total of 173 fish representing nine species were collected with nets. Carp, Cypnintto ea/42i°, were the most numerous (0.1 fish/m) followed by threadfin shad (0.05 fish/m) and channel catfish (0.03 fish/m). A summary of the netting data is presented on Table 13.

Electrofishing yielded 551 fish from 13 species. Largemouth bass

(0.332 fish/min), carp (0.29 fish/min), and bluegill (0.216 fish/min) comprised over 76 percent of electrofishing collections (Table 14).

A summary of the relative abundance of each species for each collection method is presented on Table 15. Table 11.-Numbers of each fish species collected at 57 sampling locations from Separation Rapids to Boulder Canyon, Lake Mead, Arizona -Nevada, 1978-1979. *= fish species observed but not collected. +=area sampled more than once.

STATION NAME s.. w 4.., = m S.- 1.; CV -.1C 0 -1-) U > RS CCS 0 ....-.. c al ''' U, 1 ) S7. -"" - 3 U 4- 4.)) ICI 0 E>, fIS C 4.- C.)

04 C Ira 413 .....--. 5- 3 tn 113 (.-) 4- .T. ....Y E _. , w L., .,...... --. ..1C C.) C.) 1-.. I-- a) -C1 CD C 0 ISS MS .1.- mr S. LO en N. Q) LO > LO •r- Ce 01 0 s-- al el- I.L. zr. CD • 4-• • C • to • CC/ • C...) • " 0.I 01 ei: ‘.0 (..) 00 S. 01 MS (.0 (-) Is.- 01 C 01 (r) 0- 4 >> S... et cr et RZI" C nt 0- %.0 C.) %.0 ) ;JO (I.) L0 CD kij 'V N. CLI r•••• S- CLI 04 NI 0..3 C■1 CI) 04 S.- CV C 0.1 4- 0.1 ..0 CN.1 G.1 0..1 (0 0..I CI) C\ I 0 > 0- = .1-• RS I— S- a, _c E •r— Z X X Ed) E v) X 1.-- E co E= X cz E cm X cr) x I.L.i "Antsgalor Cove" "Gill Net Cove" Lava Point God's Pocket ce ct ce ce ce ---- ce .-- ce .--- cc ---- cc ..-- cc = ce = cc ---- cc --- Lower Pierce Ferry

STATION NUMBER 1 2 3 4 5+ 6+ 7 8 9 10 11 12+ 13 14 15 16 17 18

Species COLORADO RIVER GRAND WASH

Threadfin shad 1 1 7 23 23 Rainbow trout Carp 10 10 2 1 3 1 Speckled dace 55 1 Red shiner 60 75 660 1 600 Fathead minnow 1 10 500 Razorback sucker Flannelmouth sucker 4 2 Bluehead mountain-sucker Channel catfish 1 1 1 Yellow bullhead 1 8 Black bullhead 1 Rio Grande killifish 3 30 Mosquitofish 1 50 400 1 Striped bass 7 4 3 Largemouth bass 1 3 10 1 Green sunfish 2 1 Bluegill 2 1 73 Black crappie Bluegill x green enn.Fick ik.a...... :A% Table 3luegill Largemouth bass Species Black bullhead Bluegill x Bluehead Striped bass Speckled dace Fathead Flannelmouth Black crappie Rio Grandekillifish Razorback sucker Red shiner Rainbow trout Threadfin Channel catfish Carp Mosquitofish Yellow bullhead Green sunfish nfich 11.

minoow (hybrid mountain-sucker (continued) shad green sucker

19 2021+22+23+24+2526+2728+29+303132+33+ 12 3 3 172 * 2 23614 *14 North Howland Cove 14 24 10 4 *21714 * 1 1

9631213 158 Sunfish Cove

Crappie Cove 3 9 5 GREGG BASIN 7

81011* "South Cove#1" STATION NUMBER 1 "South Cove#2" STATION NAME 2 1 9 2 "South Cove#3" 2 1 * 1

Lower Smith Bay 3 135 * 133 *4 1 4 2 26 2 4 1 UpperHualapai 10 1 2 9 LowerHualapai 34 353637+ * 1

*22 Gr TEMPLE BASIN 3 20 * 1

1 1 1

Table 11. (continued)

STATION NAME

a) S.- > W

#1" -C .1- > c.n = M CC = >1 3 = >) >1 4- M •r- >, w s- -o to CCto 4-in a) d) 1:3 co W 0)S.- 'V clo ci) 4- -C > CC C S- 4.3 -6- = -o ..-- o m m m RSs.. E= ›..., = r--. tnM (...) V) r- W W W .1-4-) >. C:) (/) MI RS (-) 3 W cf) r- -0 > c0 4- 4- CL CO I- X C 0-1 0 5- 0 0 0 0 >1 u) 4-3 S- rES 0 2 W C-) W W CD S- o--4 5.- CI) r 3 M 1, t; 4- :I9 +3 73 -F3 -F3 -8 4, 21, .— X , 0 o ,--- = = s- c o EV 0 4-)CO •Er- .0 toCU E RO .1--4-) 0 0 CO inCL) IMS 0 4-3 0 "Burton's Finger "Burton's Finger #2" Heron Point Trail Rapids Bay Lower Haystack Bay C..) "") L.1.1 M = C/) --I M M = 3 (A A. CL) CO STATION NUMBER 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

Species TEMPLE BASIN OVERTON ARM VIRGIN BASIN

Threadfin shad 1 * * 486 * 4 1217 1500 Rainbow trout Carp 7 4 9 3 7 1 8 913 9 1 9 5 2 Speckled dace * Red shiner 10 1971 675 Fathead minnow 2 Razorback sucker 1 Flannelmouth sucker Bluehead mountain-sucker Channel catfish 6 2 2 1 2 2 2 2 2 3 2 Yellow bullhead Black bullhead Rio Grande killifish Mosquitofish 4 15 585 270 Striped bass 1 1 1 2 Largemouth bass 2 * 5 3 * 4 2 5 1 Green sunfish * 3 2 1 11 1 6 1 Bluegill 21 * 5 10 1 3 Black crappie 1 Bluegill x green -IA% 39

Table 12. Summary of seine collecting data from Separation Rapids to Boulder Canyon, LakeoMead, Arizona-Nevada, 1978-1979. trace =>0.01 fish/re

Species No. Collected No. fish/m2

Red shiner 4,061 0.63

Threadfin shad 3,242 0.50

Mosquitofish 1,329 0.21

Fathead minnow 511 0.08

Bluegill 106 0.02

Speckled dace 56 0.01

Rio Grand killifish 33 0.01

Carp 30 trace

Largemouth bass 18 trace

Green sunfish 7 trace

Flannelmouth sucker 6 trace

Channel catfish 4 trace

Bluehead mountain sucker trace 40 Table 13. Rimmary of trammel and gill netting data from Separation Apids to Boulder Canyon, Lake Mead, Arizona-Nevada, 1978- 1D79. trace => 0.01 fish/hr.

Species No. Collected No. fish/hr

Carp 69 0.10

Threadfin shad 34 0.05

Channel catfish 22 0.03

Green sunfish 15 0.02

Bluegill 14 0.02

Striped bass 10 0.02

Yellow bullhead 11 0.02

Largemouth bass 5 0.01

Razorback sucker 2 trace

Black bullhead 1 trace 41

Table 14. Summary of electroshocking data from Lake Mead, Arizona-Nevada, 1978-1979. (total shocking time = 500 min.)

Ave. # fish/min. Species No. Collected shocking time

Largemouth bass 166 0.332

Carp 145 0.290

Bluegill 108 0.216

Green sunfish 48 0 .096

Channel catfish 37 0.074

Striped bass 26 0.052

Threadfin shad 9 0 .018

Black crappie 7 0 .014 Yellow bullhead 1 0.002 Rainbow trout 1 0.002 Razorback sucker 1 0.002 Red shiner 1 0.002 Bluegill x green sunfish 1 0 .002 (hybrid) Table 15. Relative abundance of 19 fish species collected from Separation Rapids to Boulder Canyon, Lake Mead, Arizona-Nevada, 1978-1979. trace =>0.1 fish/m2 or> 0.01 fish/hr

Collecting Method Seine Trammel or Gill Net Electrofishing Species Total #Collected fish/meter2 #Collected fish/hour #Collected fish/hour Collected

Red shiner 4,061 0.63 1 0.12 4,062 Threadfin shad 3,242 0.50 34 0.05 9 1.08 3,285 Mosquitofish 1,329 0.21 1,329 Fathead minnow 511 0.08 511 Carp 30 trace 69 0.10 142 17.16 242 Bluegill 106 0.02 14 0.02 101 12.12 221 Largemouth bass 18 trace 5 0.01 166 19.92 189 Green sunfish 7 trace 15 0.02 48 5.76 70 Channel catfish 4 trace 22 0.03 37 4.44 63 Speckled dace 56 0.01 56 Striped bass 10 0.02 26 3.12 36 Rio Grande killifish 33 0.01 33 Yellow bullhead 11 0.02 1 0.12 12 Black crappie 7 0.84 7 Flannelmouth sucker 6 trace 6 Razorback sucker 2 trace 1 0.12 3 Rainbow trout 1 0.12 1 Bluehead mtn sucker 1 trace 1 Black bullhead 1 trace 1 Bluegill x Green sun- 1 0.12 1 fish (hybrid) Totals 9,404 183 542 10,129 43

Disease

Most evidence of diseases of Lake Mead fishes is from NOW reports on largemouth bass and their nests. This information is not indicial that the bass is the most heavily diseased, but reflects the great deal of attention this species has received during the 45-year history of the reservoir. Recently, Roden (1978) listed the parasites occasionally found in fishes of Lakes Mead and Mohave from reports by Jonez and Sumner (1954),

Johnson (1973), Buck (1975 , 1976) and Padilla and Rosenlund - pers. corns. (Table 16). To the best of my knowledge, none of these forms have attained the numbers necessary to seriously impact the fishery.

Leeches or leech scars were observed in 79 percent of channel catfish and three percent of the largemouth bass examined during the study

(Table 17). They were typically attached to the pelvic, anal, and caudal fins, and rarely attached to the posterior dorsum and caudal peduncle of catfish. On largemouth bass they were found on the ventral fins and the lower half of the caudal fin. Probably the greatest physical damage attributed to leeches, other than blood removal, is the wound that creates an avenue for bacterial and/or fungal infections.

The anchor worm, Lanaea eyptinacel, a familiar parasite of warm-water fishes in Arizona, was noted from largemouth bass (2% of fish examined) and red shiners (0.1%). The copepod has been reported in largemouth bass, bluegill, crappie, and green sunfish during a survey of the Lake Mead fishes in the early 1950's (Jonez and Sumner

1954). It is also a common parasite of the flannelmouth and bluehead mountain suckers, the speckled dace, and the humpback chub from Colorado

River tributaries in the Grand Canyon (Carothers and Minckley 1980). 44

Table 16. List of fish parasites reported from Lakes Mead and Mohave (from Roden 1978).

Protozoa Coztia sp. Ttichodina sp. IchthyopthiAita sp.

Phycomycetes Saptotegnia sp. (water mold)

Trematoda Gykodactgu4 sp.

Cestoda Puteocephatto ambtopti (bass tapeworm)

Nematoda ContAacaecum matipapittatum

Annelida Iteinobdata sp.

Copepoda Letnaea sp. (anchor worm) 45

Table 17. Parasites of Lake Mead fishes collected from Separation Rapids to Boulder Canyon, Arizona-Nevada, 1978-1979

Fish Species Parasite Number Number Percent Infected Examined Infected Infected

Trematoda strigeid bluegill 41 19 46 metacercariae

Cestoda Pnoteaeophaews sp. largemouth bass 109 7 6

Nemotada largemouth bass 109 91 84 channel catfish 63 15 Contuccaecum sp. 24 bluegill 41 7 17

Annelida Hiudinea channel catfish 63 50* 79 largemouth bass 109 3 3

Copepoda largemouth bass Lanaea cypninaceae 109 2 2 red shiners 4,062 35 0.1

*Fish considered infected if leech pock scars were evident. 46

The ancbor worm attaches at the base of the dorsal and caudal fins of both species. These areas seem to be preferred because the fins offer a certain amount of protection from being dislodged. Although there is evidence that indicates the copepod may cause blindness in rainbow trout when they attach in or near the eyes (Uzmann and Rayner 1965), unless they reach epidemic numbers, their damage to fishes is ordinarily minor.

The import of the external parasitism of the Lake Mead fishes can not be completely known without further information, but probably is minimal. One consideration must be the fact that parasites leave red

inflamed areas and ulcer-like lesions that are obvious to the angler.

Certainly, a number of parasitized fish never reach the creel when they

are returned by leary anglers. In fact, these two ectoparasites may

diminish the aesthetic character of a fish, but are generally of little

consequence to its edible qualities.

Three internal parasites were identified from the fishes of Lake

Mead: a bass tapeworm, Ptoteocephatta sp., a roundworm, Contkacaecum

sp.,and a larval fluke. The tapeworm was found only in the largemouth

bass in six percent of those fish examined. This is generally regarded

as one of the most damaging tapeworms since both the intermediate and

the final host is the fish (Sinderman 1953, Meyer 1954, Morrison 1957).

Bass usually acquire the parasite when they are less than 50 mm TL.

During this time they are planktivores consuming large quantities of

copepod crustaceans which are the tapeworms' first intermediate host.

If the young bass are not infected, as adults they are apt to ingest

smaller fish that are carrying the adult tapeworms.

The most damaging effect of the tapeworm usually is inflicted by 47 the larval stages, plerocercoids, in the viscera. The results may be an adhesion or matting of the viscera, or even more serious, an infection of the reproductive tissue causing sterility. Plerocercoids may spread within the body cavity until 50 percent of the total weight is that of the tapeworm. In this situation, the reproductive organs become degener- ate and eventually non-functional (Dence 1958).

The most common endoparasite was a coiled, white roundworm, Contta- caecum sp.,found in largemouth bass (84% of fish examined), channel catfish (24%) and bluegill (14%). Conttamecum was most abundant in the viscera of largemouth bass from the anterior esophagus to the anus arid most heavily concentrated on the mesentary of the stomach and pyloric caeca. The number of worms per fish ranged from 3 to well over 100 and was directly related to the size (age) of the fish.

The life cycle of the roundworm includes fish-eating birds as an adult host. The adults are introduced into the water through the feces and the roundworm larvae are hatched in the water and eaten by young fish. Growth of the roundworm is very rapid based on a single young- of-the-year (93 mm TL) that contained six worms that completely filled the peritoneum and noticeably distended the belly.

Larval flukes were observed in the liver tissue of almost half (46%) of the bluegill examined. The metacercariae are common to Arizona centrarchids of the genus Leporm&s, but are apparently less common in the

"basses". In small lakes they are capable of infecting virtually all of sunfishes with little or no obvious inconvenience to the fish. The degree of infestation of Lake Mead bluegill is not nearly as extensive as populations in other Arizona waters. The number of metacercariae per 48

fish typically ranged from 6 to 15.

The life cycle of a strigeid trematodes ordinarily involves a snail as the first intermediate host, a fish as the second host and finally a fish-eating bird. In a few cases, the final host may be a fish-eating mammal or a fish (Hugghins 1954). The harmful effects of metacercariae are many, including: abnormalities in meristics (Hubbs 1927); suscepti- bility to winter-kill (Elliott and Russert 1949) and predation (Hunter

1942); stunting and emaciation (Cross 1935; Hugghins 1972); blindness, and eventually death (Hoffman 1956; Wales 1958).

Life Histories

NATIVE SPECIES

Speckled Dace

The speckleddace, Rhinichthyu oiscauz, is a small (usually 4:10 cm IL), slender minnow with a thick caudal peduncle, a pointed snout, and a distinctive, small subterminal mouth. Rhinichthys means snout-fish and the small mouth inspired oacutuis which means kissing. They are highly variable in color, usually with blotches with brown and brown-black on the sides.

Some forms may show a distinctive lateral band. This dace prefers shallow streams, rivers and desert spring outflows over rocky bottoms. They are quite adaptable and may be successful in lakes or intermittent streams that reach 33°C (John 1964).

The speckled dace was first described in 1851 from 10 specimens taken from Bobocomori Creek, a tributary of the San Pedro River in southeastern Arizona. The original range of the speckled dace was west of the Rocky Mountains from Washington and Idaho to southern California 49

and Arizona. It is one of the few native minnows that has been able to

resist man's endeavors to manipulate waters of the southwest and as a

result, is common and widespread in Arizona, Colorado, Nevada, Utah and

Wyoming. In Arizona waters it generally is most abundant over 2,500

feet.

Distribution and abundance

As with many native minnows endemic to and abundant in the Colorado

River and its tributaries, the speckled dace has found the reservoir

environment intolerable. They are still common in tributaries of the

Colorado River above Lake Mead but rarely enter the main channel. Their

distribution above Lake Mead in Arizona is included in reports by McKee

(1930), Minckley and Blinn (1975), Holden and Stalnaker (1975), Suttkus

et al. (1976), Carothers and Minckley (1980), and McCall (1980). It was reported from Las Vegas Creek, a flood tributary of Lake Mead in the

late 1940's (Hubbs and Miller 1948).

A total of 56 speckled dace was collected from Lake Mead during

1977 and 1978. These were taken on two separate occasions at the confluence of Spencer Creek and the Colorado River. Dace were seined from pools and riffles over sandy bottoms. Dace and red shiners were collected simultaneously and both species seemed to prefer the cover provided by attached filamentous algae below eddies. The absence of dace

in these collections in September 1978 and March 1979 may be partially explained by the fact that only the lower 100 m of the creek was surveyed and they are most abundant in the upper portion of the Creek

(Deacon and Baker 1976). 50

Food habits

The subterminal mouth suggests that the speckled dace is best suited

as a bottom feeder The relatively short intestine and the structure of the

pharyngeal teeth are adaptations that make them well adapted for utilizing

small bottom insects. Other food items normally found in the diet are

zooplankton and surface insects, and during the winter months algae com-

prises an important food when the insects are not as available. The diet

of speckled dace in Spencer Creek is dominately midge and blackfly larvae

with supplemental food items including caddisflied and mayflies (Wilde 1976).

In the Colorado River above the Lake Mead Recreation Area, terrestrial

insects are also utilized in small to moderate quantities during the spring

and summer.

the main river but comprise less than 10 percent of the diet. Several

of the dominant forms are lady beetle (Coccinellidae), black flies, an

Ichneumonid wasp (Ichneumonidae) and ants (Formicidae). The diet changes

with the season with dipteran larvae commonly consumed during the winter, and scuds and mayfly nymphs during the summer months (Carothers and Minckley

1980).

Reproduction

Speckled dace spawn in Spencer Creek in the spring and early summer

as water temperature approaches 18-20°C. In intermittent streams in

Arizona, spawning behavior may be induced during spate with peak acitvity

during early spring fun-off and later in the summer when creeks are flooded

from the summer rains. Although the nuptial behavior for this species

is not ducumented, observations of most of the other members of the

genus Rhillichythes usually involves a single breeding pair. The male is 51

tuberculated along the axils of the paired fins and anal fin and lower

lobe of the caudal becomes dark orange or scarlet. Breeding colors can

also be seen around the mouth and on the upper part of the operculum.

Spawning generally occurs below riffles on gravel or coarse sand where

the male removes algae and detritus and smooths out the bottom with his

fins and snout. He then approaches the female, nudging her with his head

and body. She discharges her eggs close to the bottom as the male simul-

taneously discharges sperm while rapidly vibrating his caudal peduncle.

After a short period they both separate. The eggs hatch in six days (18-

19°C) and the larval fish emerge from the gravel in about one week (Jahn

1963).

Age and growth

Speckled dace typically live to three years of age, or perhaps four

in southern Arizona (John 1964), and rarely exceed 8 cm total length.

Scales are first detected at 13 mm TL and the annuli are identified by

one set of circuli tangent to those of the previous year, or one or two

narrow weakly marked circuli (Jhingran 1948). The method of aging may

be less accurate in dace than other species since growth probably con-

tinues, at least to some extent, during the winter months. They may reach

35 mm by the end of the first year and continue to grow about 15 mm per year, with females growing slightly faster than males (Baker 1967, Jhingran

1948).

Present status and significance to the fishery

Speckled dace were found only at one location in the Lake Mead

Recreation Area near the mouth of Spencer Creek in the Colorado River.

The dace is unimportant to the fishery contributing little to the food

pyramid due to its habits and habitat preferences. In waters where 52 they are numerous, most are unavailable as a forage fish seeking secluded areas near rocks and debris and their nocturnal feeding behavior make them even more unavailable to sight-feeding predators.

Razorback sucker

The razorbck sucker, Xy4auchen texanuz, is a relatively large sucker with large, soMbwhat compressed head, small eyes, and a sharply-edged keel on the nape. XyAmichen translates to "razor nape" but the derivation of texama is not understood since this species does not occur in Texas.

The large mouth has moderately developed labial papillae with a deep median cleft separating the two halves of the lower lip. Razorbacks are brown to brown-black on the dorsum becoming yellow or orange on the belly.

Breeding males are darker on the dorsum and more brilliantly colored on the ventral surface. Males develop tubercles on the dorsal and anal fins and the peduncle. The genital papillae of breeding females becomes enlarged and convulted often extending 7-8 cm below the ventral plane.

The razorback sucker was historically common in the larger streams of the Gila River system and the mainstream Colorado River. The sucker was once a staple of Indians living near the Colorado River and continued

to be utilized as a food fish after settlement of the Southwest. They

were sold as "buffalo" in Tombstone, Arizona, around 1880. These fish are typically very docile and are not easily alarmed. Occasionally,nesting razorbacks allow SCUBA divers to approach and touch them (Jim Brooks,

AGFD, pers. comm.).

Distribution and abundance

Razorback suckers are rare in Lake Mead as evidenced by their scarcity

in scientific collections and the few verifiable observations. T

In February, 1967, AGED electrofished selected areas of Lake Mead col-

lecting 810 fish including eight razorback suckers. The behavior of two

adult suckers located near the Temple was recorded with underwater photo-

graphy (16 mm) by AGED in 1974. Only three razorbacks were collected during

this survey. The first was taken while electrofishing Haystack Bay the night

of 26 July 1978 (Table 12). This was an adult male (552 mm TL) fish taken

in about 4 m of water near the shore. The other two specimens were gravid

females (667 and 670 mm TL) collected from the back of Little Bitter Wash

in the upper Overton Arm. A close examination of the external surface,

fins, oral cavity, and gill filaments revealed no evidence of ectoparasites

or parasite scars. The fish were noticeably sluggish when removed from

the water but otherwise appeared to be healthy.

Age and growth

The age of razorback suckers at maturity and the longevity is still

unknown, although they are presumed to be a relatively long-lived fish.

Any attempts to examine age and growth patterns of the sucker would be dif-

ficult since successful reproduction in recent years is yet to be docu-

mented. Most of the specimens taken from Lake Mohave, Arizona, by W. L.

Minckley have been relatively large (70 - 73 cm) and are believed to

"...represent the same general size(age) class(es)..." The smallest taken

from the lake was 30.5 cm SL and in excess of seven years of age (Gustafson

1974). The three suckers collected from Lake Mead averaged 629.3 mm TL

and 2.78 kg with a mean condition factor of 1.08 (Table 19).

Reproduction

Forty adult suckers were collected from Lake Mohave in March 1974,

in a joint federal and state recovery effort. Eight of these fish were Table 18. Summary of observations and collections of razorback suckers in Lake Mead, Arizona-Nevada, 1967-1979. ND = No Data.

Date No. fish Len th mm Wei ht k Sex Location

1967 8 =24 T.L. R=2.3 FL. ND ND n=6) (n=6)__Ì 243 3.0 ND ND

\260 3.3 ND ND

1977 1 ND ND ND South Cove

14 Nov. 1977 1 550 T.L. 1.7 ND Smith Bay

502 F.L.

23 Feb. 1978 2 ND ND ND Wagon Trail Bay

23 Feb. 1978 2 ND ND ND South Cove

27 July 1978 1 ND ND ND Lower Hualapai Bay

26 July 1978 1 552 T.L. 1.73 male Lower Haystack Bay

12 March 1979 1 ND ND ND Little Bitter Wash

13 March 1979 1 667 T.L. 3.18 female Little Bitter Wash

13 March 1979 1 670 T.L. 3.4 female Little Bitter Wash

19 June 1979 1 ND ND ND Temple 55

Table 19. Length, weight, and condition factor data of Lake Mead fishes collected from Separation Rapids to Boulder Canyon, Lake Mead, Arizona-Nevada, 1978-79.

Number Total Weight Condition Species of Fish Length (mm) (gm) factor (KTO

Threadfin shad 3,285 = 121.8 = 29.0 = 1.6 (85 - 154) Rainbow trout 1 543 545 0.34 Carp 242 x = 413.3 x = 992.9 x = 1.34 (74 - 586) (3 - 2495) (0.53 - 2.20) Razorback sucker 3 = 629.3 T= 2776.7 = 1.08 (551 - 670) (1730 - 3400) (1.03 - 1.13) Channel catfish 63 T = 337.8 -x- = 363.8 = 0.82 (114 - 552) (20 - 1640) (0.44 - 1.35) Yellow bullhead 12 = 236.7 = 217.2 x = 1.62 (192 - 242) (125 - 255) (1.44 - 1.78) Black bullhead 1 245 210 1.43 Striped bass 36 = 270.7 = 323.4 T= 1.00 (103 - 540) (8 - 1200) (0.73 - 1.31) - Largemouth bass 189 i = 271.8 = 381.6 5( = 1.28 (6 - 490) (0.8 - 2272) (0.51 - 1.99) Green sunfish 70 x= 96.7 3C = 34.4 = 1.53 (49 - 180) (40 - 90) (1.36 - 1.82) _ -- Bluegill 221 )C = 19.0 x = 34.4 = 2.04 (14 - 195) Black crappie 7 i= 289.1 T = 422.2 T = 1.21 (110 - 369) (120 - 682) (0.85 - 1.59) 56 sacrificed for disease inspection and the remaining 32 transported to the Arizona State Hatchery at Page Springs, Arizona. The goal of the study was to provide a management program to perpetuate this native species. Approximately 5,000 ova were stripped from gravid females, fertilized with sperm from two males, and transported to the Willow

Beach National hsh Hatchery. From samples preserved daily, Gustafson

(1974) was abld to observe embryological development for the first month of life.

The color (Douglas 1952, Minckley 1973, Gustafson 1974) and tuber- culation (Douglas 1952; Bronson 1961, 1966; Minckley 1973; Gustafson

1974) of the razorback sucker are sexually dimorphic during the reproductive season. Four other sex recognition characters are: 1. size

(both total and standard length); 2. pelvic fin lengths; 3. anal fin length; 4. length and morphology of urogenital papillae. A description of these characteristics is discussed by Gustafson (1974). The fecundity of the razorback sucker has not been completely determined in the lower

Colorado River Basin partially due to the unavailability of a series of age classes.

Razorback suckers have been observed attempting to spawn in the

Overton Arm of Lake Mead for the past several years (Cal Allan, NDW, pers. comm.). The spawning ritual is described from observations from the shore of a small bay near Needles Boat landing on Lake Havasu in the spring of 1950. Several males escort the female in a small circle about

1.2 m in diameter. The males remain close to the female while moving in a clockwise direction and prodding her with their heads from both 57

sides, at a point just behind her nuchal hump. The actual spawning act

was obscured by rising silt but apparently occurred within 39-45 seconds.

The fish then separate and move away from the area (Douglas 1952). The female may spawn with several of her escorts.

Razorbacks apparently spawn in Lake Mohave from November to June

0 0 (Gustafson 1974) when air temperatures range from 17 to 21 with a mean

0 o of 19.4°C and surface temperatures range from 14.5 to 18 C with a mean of 16.8°C. At present, there is no evidence to indicate razorback suckers successfully reproduce in Lake Mead. If spawning does occur it is probably from March to late June when water temperatures are similar to those measured during the spawning season in Lake Mohave.

Food habits

The feeding behavior of a single female was observed in Lake Mead from a boat in the back of Little Bitter Wash. The sucker was feeding on bottom debris while trailing a school of 15-20 carp. She was foraging about 30 cm above a sandy bottom in water about 1.5 m deep. Forward movement was slow, powered by short, steady oscillations of the caudal fin. At 2-3 m intervals the caudal movement would stop and the head would dip until the fish was only a few centimeters from the bottom when the iip would quickly extend to "suck up" bottom detritus. The foraging path apparently was more influenced by the direction of the pilot school of carp than searching behavior for food items.

To date, there are no detailed food habits studies on xutauchen.

In Lake Mead they take a variety of foods including algae, insects and detritus (Jonez and Sumner 1954). Razorbacks also consume planktonic crustaceans. The following observation was recorded from Lake Mohave: 58

Feeding activities were observed in about six meters of water. The fish moved with their mouths projecting forward and with a "bouncing" up-and-down pattern produced by slow, alternating sweeps of the caudal fin. The pectoral fins were held stiffly, extended, producing a plane effect, and little lateral movement of the head was evident, perhaps as a result of the keel-like anterodorsal surface which may act as a stabilizer(Minckley 1973).

Present status and significance to the fishery

Razorback suckers are rare in Lake Mead and are in danger of being completely extirpated from the reservoir in the near future. The decline of razorback sucker and other indigenous fishes in Lake Mead and other Colorado River impoundments is directly related to man's activities (Dill 1944; Miller 1946, 1955; and Beland 1953). With the construction of Glen Canyon Dam in 1964, proximate downstream water temperatures were lowered to a point that prohibited successful reproduction. Not only was there an abrupt change in the aquatic environment

but also numerous exotic fishes were released to creat sport fisheries which increased competition for food and space. Several of these introduced species were voracious predators which undoubtedly impacted any recruitment from warm-water tributaries. Another factor contributing to the decline of the species is genetic dilution with Catcpstomm. Razor- backs are known to hybridize with C. in441,4:4 and C. tatipinniz. The latter is recorded above Lake Mead in the Colorado River and it is suggested there is a minimum 10 percent hybridization with Catostomm6 sp. in Lake Mohave (Gustafson 1974).

Assuming they were able to reproduce during the filling of the reservoir in the late 1930's, subsequent fluctuating water levels in

Lake Mead may have contributed to the population decline by destroying 59

eggs along the shore. The dessication of razorback eggs was observed in

1975 below Hoover Dam when water levels dropped more than a meter (Gus-

tafson 1974). W. L. Minckley suggests apparent failure of razorback suckers

to reproduce in Lake Mohave may be due to predator pressure. He observed several razorbacks spawning and found eggs along the rocks below Hoover

Dam but when the same areas was surveyed about two weeks later numerous centrarchids were collected but no razorback larvae (W. L. Minckley, pers. comm.).

In January, 1979, the Colorado Division of Wildlife elevated the razorback sucker from threatened to endangered status in Colorado. This reclassification occurred when age class data indicated this species was not successfully reproducing (Dave Langlois, CDW, pers. comm.).

The razorback sucker is protected by the NDW and listed as rare, which translates to "...(the razorback sucker) although not presently threatened with extinction, is in such small numbers throughout its range that it may be endangered if its environment worsens. Close watch of its status is necessary". AGFD lists the razorback sucker under

Group III of the Threatened and Unique Wildlife of Arizona (AGFD 1978) which states "...(the razorback sucker) may be in jeopardy in the foreseeable future". Recently, AGFD amended their fishing regulations to include the razorback sucker as a protected fish in Arizona (effective 1

April 1980). The USFWS has proposed the razorback sucker for listing as threatened in 1978 (USFWS 1978) but it now seems the species will not be 60 listed in the near future (Jim Williams, USFWS, pers. corn.).

Flannelmouth sucker

The flannelmouth sucker, CATOZTOMWS TATIPPIN4:4, is a relatively large catostomid weighing over 1.6 kg (McDonald and Dotson 1960) and reaching a total length of 0.5 m (Bosley 1960; Minckley 1973). The name

TITIPPIRAZ means broadfin which adequately describes the distinctively enlarged fins. The subfusiform body is slim with medium-sized scales and the head is proportionately small. This species was once abundant throughout the Colorado River drainage in Arizona, Nevada, New Mexico,

Utah, Colorado and Wyoming, and was historically important to the Indians providing an abundant food source (Sigler and Miller 1963). In recent years, its range has been reduced largely because of manipulation of the waters of the Colorado River and its tributaries.

Distribution and abundance

C. L. Hubbs first noted this species in Lake Mead from a bait tank in 1938. Later in 1950, 0. L. Wallis and R. R. Miller and party also found them in bait shops (Miller 1952). Most records of the sucker from the lower Colorado basin are from the Virgin River and the mainstream Colorado River above Lake Mead (Tanner 1932; Miller 1946b; Caro- thers and Minckley, 1980).

I have observed them to be common in the tributaries of the upper reaches Colorado River from Glen Canyon Dam to Phantom Ranch and they have been frequeltly collected throughout the Colorado River in the

Grand Canyon (Cdtothers and Minckley 1980). In the Lake Mead Recreation

Area, congregations of flannelmouth suckers are recorded from the mouth

of Spencer Creek (river mile 246) (Suttkus et al. 1976) and Surprise 61

Canyon (river mile 248.5) (Deacon and Baker 1976).

Flannelmouth suckers were not collected from these tributaries in

1978-1979, but there were two yearling fish seined from a shallow backwater

of the main river just below the Bat Caves (Station #9, "The Sink", river mile 267.5). To the best of my knowledge, this location is the furthest down the Colorado River the sucker has been recorded in the Lake Mead

Recreation Area.

Reproduction

Of the eight native species that were once common in the Colorado

River above the reservoir, the flannelmouth is one of only two species that presently inhabits the main river in any numbers. Spawning probably occurs in Spencer Creek, or perhaps Surprise Canyon in early spring.

In other warm water tributaries of the Colorado River, tuberculated males enter the tributaries in early April and spawning continues into June.

The flannelmouth readily hybridizes with other catostomid genera including Pantoztews and XyAauchen. Hybrids of flannelmouth and the Gila mountain-sucker, P.ctatki, (Baird and Girard) (reported as P. detphinuis utahenza) were collected from the Virgin River in Utah in the early 1940's (Hubbs and Johnson 1943), and there is some hybridization with the Utah sucker, C. akdero, in a tributary of the lower Virgin River (Minckley 1973). Prior to the 1950's when razorback suckers were abundant, flannelmouth and razorback hybridization was not uncommon (Hubbs and Miller 1953). An occasional hybrid was collected from the Colorado

River above Lake Mead in the early 1970's (Holden and Stalnaker 1975,

Suttkus et al. 1976) but few have been taken in recent years (see pages

158-159). 62

Age and growth

Until recently, age and growth studies of flannelmouth suckers in the

Colorado River were from populations in the upper basin (Wiltzius 1976,

McAda 1977). The findings of these studies indicate suckers from the

Green River in Utah live to an age of about six years and reach a total length of over 36 cm. The average growth per year is 51.8 mm with the greatest growth (130 mm) between year classes II and III (McDonald and

Dotson 1960).

In the Colorado River in Arizona, flannelmouth suckers may live 10 years or longer and are uncommonly large reaching total lengths of over

60 cm. Using the opercle method to age fish, Usher et al. (1980) found that the average annual growth increment for this first year was 121.6 mm.

The following year growth was reduced to about half (63.5 mm). They theor- ized that the accelerated growth of Colorado River flannelmouths during the first year of life is related to the warmer side streams and higher benthic productivity (Carothers and Minckley 1980). When these fish enter the consistently cold water of the Colorado River (7-10°C) the annual growth increments steadily decline.

Food habits

The results of a recent food habits study indicates the flannelmouth suckers of the Colorado River in Arizona consume large numbers of aquatic invertebrates. Scuds and immature dipterans (mostly blackflies) were the dominant invertebrates in the diet. These two food items were mostly utilized during the winter months, comprising 25 to 73 percent of the winter and fall diets, respectively. Other invertebrate food items 63 included micro-caddisfly larvae (Hydroptilidae), a pyralid moth larvae, a riffle beetle larvae (Elmidae), a crane fly larvae (Tipulidae), water mites (Sperchonidae), and a net-winged midge larvae (Blephariceridae).

Adult ants, leafhoppers, and planthoppers were also consumed, probably after they had settled to the river bottom (Carothers and Minckley

1980).

Present status and significance to the Fishery

Flannelmouth suckers do not inhabit the main reservoir and are rare in the Lake Mead Recreation Area above Pierce Ferry. In other Arizona waters they are not a popular sport fish except for bow and arrow fishermen, and even then they are usually taken for sport and not eaten. At present, the flannelmouth sucker has little, if any, importance to the

Lake Mead fishery.

Bluehead mountain-sucker

Originally established by Cope in 1875, the genus Panto4tec4 described western catostomids inhabiting mountain streams and character- istically having thick skulls and cutting edges on both jaws. The suckers inhabiting the mainstream Colorado River in the Lake Mead Recrea- tion Area are morphologically unique. These fish are extremely specialized with a narrow, long caudal peduncle similar to that of Oita etegans and to a lesser degree Gita cypha. The wide variation in the complex morphology of species belonging to the genera Catutoma and Pantuteca which has resulted in differences of opinion concerning the taxonomy of the bluehead mountain-sucker. The two genera Panto4teus and Catutomita were synonymized as Catutomws in 1966 (Smith 1966) which is currently 64 recognized by the American Fisheries Society. Smith based his judg- ment principally from similarities between Pontoztem6 caumbianto from the Columbia river system and Cato4tomws ptebeicus from the southwest U. S. and Mexico. Some argument exists that ptebeiu4 is not typical of the genus Catoztomus but, in fact, shows intermediate characteristics between

Catoztomws and Pantoztua. Another criterion used as evidence to unite these genera is the high frequency of hybridization. Intra-generic crosses are not uncommon between species of the two genera (Koehn and

Rasmussen 1967; Koehn 1969, 1970). This introgression is supported by blood protein similarities but it is not obvious in morphological characters of western catostomids (Minckley 1973).

Distribution and abundance

The bluehead mountain-sucker is not found in the Lake Mead Recrea- tion Area below Pierce Ferry. They are common in the upper Colorado River from Glen Canyon Dam to Lee's Ferry (McCall 1980a), and they are second in abundance of the native fishes inhabiting the Colorado River and its tributaries in the Grand Canyon (Carothers and Minckley 1980). Bluehead suckers are able to tolerate the cold water of the Colorado River but the few collection records from the main river below Separation Rapids suggests they may congregate, at least seasonally, near the warm water of Spencer

Creek and Surprise Canyon. They have been collected from Spencer Creek in 1955 as far as 100 yards from the confluence and two specimens were taken during a survey in 1976; one from Surprise Canyon and the other from a side pool approximately 8 km below the canyon (river mile 267.5)

(Deacon and Baker 1976). Only one speciman was collected during this survey; a young-of-the-year fish (62 mm TL) that was seined approximately 65

30 m from the mouth of Spencer Creek on 6 December 1978.

Reproduction

A number of suckers are probably sexually mature by their second summer at a length of 135-145 mm TL and most are mature by their fifth year. As waters warm in April and May, they enter the Colorado River tributaries above the lake to spawn. Minckley (1978) reports water temperatures of 19.5°C may induce spawning behavior. Spawning presumably takes place over gravel shoals and riffles; although the breeding behavior is yet to be documented. Fecundity estimates range from 5,492 to .

9,509 ova per female, and gonadal-somatic indices range from 3.7 to 11.2 for fish taken in the main river and 3.7 and 6.9 for fish collected in tributary streams (Carothers and Minckley, 1980).

Age and growth

Usher et al. (1980) aged suckers from annuli on opercle covers and found the fish live to an age of at least eight years reaching 397 mm

TL. The greatest growth occurs during the first year (69.3 mm) followed by a rapid decline in age class II and a steady decrease annual growth in subsequent years. There is no significant difference in the size of male and female fish until age class III when males begin to grow more slowly.

Food habits

The sharp cartilaginous scraping edges of the jaws and the relatively long intestine are morphological characteristics suggesting this species is well adapted for a herbivorous diet. However, the bluehead suckers in the Colorado River in Arizona consume large quantities of aquatic insects (primarily midge and blackfly pupae) (Carothers and Minckley 1980). 66

This preferefice for insects is atypical for mountain suckers since plant

material is usually the most important component of diet. Presumably,

numerous invertebrates are ingested while scraping filamentous algae

and diatoms from rocks and other hard surfaces.

Present status and significance to the fishery

The bluehead mountain-sucker does not occur in the main reservoir

and is rare in the Colorado River Separation Rapids and Pierce Ferry.

Although the flesh of this species is slightly more bony than other more

popular species, it is well flavored. Some Indian tribes actually prefer

suckers to trout as a food (Hubbs and Wallis 1948). They are of little

value as a sport fish as they are generally difficult to catch and

are not considered a fighting fish when hooked. Other members of the

sucker family provide sport for bow and arrow fishermen but the

bluehead does not reach the size that would make them attractive to bow

and arrow enthusiasts. In some situations they may contribute to sport

,fisheries as a forage fish, but they occur in so few numbers in the

Lake Mead Recreation Area to be of any significance to the fishery.

INTRODUCED SPECIES

Threadfin shad

Threadfin shad, Donozoma petenen6e, are small thin fish that are

easily identified by the single blackspot behind and slightly above the

operculum, and the elongated final ray of the dorsal fin. The etymology

of Do4o-4oma means "lance-body" referring to the eelike larvae and peteneri6e 67

is derived from Lake Peten, Guatemala, where the first specimens were described.

The threadfin shad is the only representative of the family Clu- peidae (herring and shad) that occurs in Arizona and Nevada. The native range of this species is from the confluence of the Ohio and Mississippi

Rivers south to the Gulf Coast, east to Florida, and west to the Yucatan

Peninsula of Mexico (Minckley and Krumholz 1960). They were first introduced in the Southwest as a result of a tri-state agreement among

Arizona, California and Nevada.

Distribution and abundance

In 1954, the original stock of Mississippi threadfin shad, D. p. atchaliatayae, was flown from Kentucky Lake, Tennessee River, Tennessee and released into the Overton Arm of Lake Mead to provide a forage fish for the largemouth bass. This species was selected for Lake Mead and other reservoirs along the Colorado River as it appeared to satisfy the following criteria: (1) small size, (2) prolific, (3) habitat needs similar to those of the largemouth bass, (4) capability to do well in

Lake Mead, and (5) non-competitive feeding habits. Additionally they are a schooling species that prefer open water which makes them an ideal forage fish for the striped bass. In just one year the original plant had reproduced and spread throughout the lake. By 1956, supplemented by releases in Lake Havasu (Kimsey et al. 1957), threadfin shad were found along the mainstream Colorado River from upper Lake Mead to

Mexico (Burns 1966) and in most of the canals that connected to the

Colorado mainstream (Johnson 1969).

They are numerous and widespread in Lake Mead. A total of 3,285 68

shad were collected with seines, gill nets and electrofishing gear. They

were second in abundance to red shiners (4,062) in all fish collections.

Large schools of shad were observed throughout the lake below Pierce Ferry

from June to September. The greatest concentration of shad was found

in the open water below the mouths of the Virgin and Moapa Rivers.

They are rarely found above Pierce Ferry; a few are infrequently

observed in the river and have been collected below the "Bat Cave" (river

mile 422.1) and at the mouth of Spencer Creek (river mile 442.6). The

paucity of suitable food items combined with cold, turbid water restricts

the movement of shad into the Colorado River in the Grand Canyon.

Reproduction

Threadfin shad may spawn at the end of their first summer but most reproduce when they reach an age of two years. When water temperature reaches about 21°C, shad move into shallow water a few meters from shore.

In California reservoirs spawning activities have been reported to take

place at 14 to 18°C (Rawstron 1964). They may use submersed or floating plants and debris as substrate for egg deposition. Males harass the

larger, distended females by swimming erratically their their flanks. A

female separates from the school and swims toward what is presumed to be a pre-selected site. She is escorted by 2 to 20 males who are often thrown completely from the water as she exudes eggs with violent lateral body movements. The attending males release sperm during the frequency which

lasts from one to five seconds. The males remain close to the female who

either spawns again on the same substrate, seeks a new spawning area or

returns to the main school. More detailed accounts of this spawning 69

behavior are described by Berry et al (1956), Kimsey et al. (1957),

Gerdes and McConnell (1963), Sheldon (1964), Johnson (1969, 1971) and others.

In Lake Mead, gonadal development begins in March and peak reproduction takes place in April and June. Yearling adults reach maturity later in the summer and release their ova by July. Generally, there is no further development of gonadal tissue for first-year spawners until the following summer (Deacon et al. 1972). There may be a secondary peak in reprodattive activity in late October or earlyNovember.. The number of ova Ohoduced by a single female ranges from about 800 to 1,650 for shad in two Arizona reservoirs (Johnson 1971) and may reach as high as

21,000 for shad in the southern U. S. (Finacane 1965). The fertilized eggs sink to the bottom where they adhere to the debris, or in open water, sink to a depth where the water equals the density of the eggs. Hatch- o ' ing occurs in three to four days at water temperatures from 24-27 C

(Sheldon 1964) and four to five days at 20°C (Kimsey 1958). The yolk sac of the eel-like planktonic larvae is absorbed in about three days and the metamorphosis to adult occurs at about 1 to 1.5 cm TL (Burns

1966).

Age and growth

Shad are relatively short-lived, rarely living three years. Annual growth patterns are 3.5-5.0 cm for the first year of life, 3.0-4,5 cm the second and 4.5-7.0 cm the third year. Total lengths of shad in

Lake Mead rarely exceed 15.0 cm TL (Deacon et al. 1972) and are generally less than 12-13 cm TL. Shad collected during the 1978-79 survey ranged from8.5 to 15.4 cm TL with an average 12.2 cm TL. Growth is 70

greatest in southern reservoirs in which shad often reach 33 cm TL. The

growth rates for males and females is fairly constant but differential

selective mortality may account for a greater number of large females

(Minckley 1973). The average condition factor for Lake Mead shad was 1.6

(Table 19).

Food habits

Shad are obligate, non-selective planktivores that strain plankton

and detritus with their gill rakers. Food habits studies have shown the

relative proportion of planktonic food items in the stomach is closely

similar to that in the water (turner 1966). Over 31 genera of food

items have been identified from shad stomachs in Lake Mead including

plant debris and phytoplankton which were common in the diet throughout

the year (Deacon et al. 1972). Sand particles become more common in

the diet as shad move into the litterol zone during the summer months.

Undoubtedly the sand aids the grinding and digestion processes.

Present status and significance to the fishery

Threadfin shad are legal baitfish in both Arizona and Nevada. Al-

though I have not observed them in any of the bait shops surrounding

Lake Mead, they are probably used to some extent (Espinosa and Deacon

1969). They are a vital forage species for largemouth bass, striped bass

and channel catfish, and are also important in the diet of black crappie

(Deacon et al. 1972) and trout (NDFG 1976). Their population dynamics

and precise interactions with other fish species remains undetermined.

It has been suggested that massive swarms of shad may influence other species by suppressing reproduction or survival; for instance, Millet (1971) reported that competition with largemouth bass 71

fry for plankton suppresses growth rates. On the other hand, Roden

(1978) theorizes that there is very little competition between the shad which is an obligate planktivore and a facultative planktivore such as

the largemouth bass fry. At present, there are not enough data on the

life history of the shad to draw conclusions concerning the inter- relationships with other species; the exception is the established critical role of the shad in the food chains of the large piscivores.

Rainbow trout

Rainbow trout are the most widely distributed member of the genus

Satmo in the Southwest. The trout, Satmo gai/Ldnuti, derives its scien-

tific mire from the ancient Latin verb UTTMO which means "to leap".

GAI4DNE4I is named after Dr. Meredith Gairdner, a naturalist who assis-

ted Sir John Richardson in collecting fishes from the Columbia River.

They are easily identified as a silver colored trout with black spots on the back and dorsal fins, and a pink or often red lateral band. The posterior edges of the opercula are often rimmed with red, the back is an olive green to brown and the belly is generally white or silver-white.

There is a great variability in color patterns and meristic characteristics of rainbow trout. Stream populations are generally darker with more spots than lake or salt-water populations. Young fish have 8 to

13 parr marks on the sides, 5 to 6 dark marks on the top of the head and dorsal fin. The edges of the dorsal and anal fin are white or light orange and there are few or no black spots on the tail (McPhail and Lindsey 1970).

The trout I have examined from the Colorado River above the reservoir rarely show the same colors or color patters. Much of the color 72 variation can be attributed to phenotypic responses to the diet, geographic location, or several other determinates such as age or spawning condition. However, the paramount factors responsible for the highly variable color patterns and body shapes of Colorado River trout are genetic. Hatch- ery-stocked trout are reared from a hodgepodge of eggs and broodstock from widely dispersed hatcheries throughout the Southwest. Intergrading of galtdnal morphotypes continues in stocked waters with local populations of "wild" fish that may have attained distinct characteristics. The in- discriminant mixing of rainbow genotypes in the hatcheries and in the field certainly ',resents a formidable challenge to a fish taxonomist. In Califorinia, foe instance, there are at least six subspecies of gal/wine/Li: the anadromous steelhead rainbow, S. g. gal/wine/Li; the Kamloops rainbow, S. g. kamao0; the Shasta rainbow, S. g. ztonei; the Kern River rainbow, S. g. glacial; the Eagle Lake rainbow, S. g. aquiblum; and the Royal silver rainbow, S. g. 'Legal's. Variability of Colorado River rainbow trout will become even more interesting with the continued releases of Lahontan cutthroat trout, S. ctakki henzhawl, above Lee's Ferry. Distribution and abundance

Rainbow trout were established in Lake Mead prior to the first documented introduction by the NDW in 1969. The origin of the initial rainbow trout stock is undetermined but an unofficial report from James Jordan of Boulder City, Nevada, stated that a number of unidentified trout were released into Lake Mead due to the loss of an election bet. One of the first reports of rainbow trout in the reservoir was in 1943 (Moffett 1943) and by the early 1950's anglers were taking trout up to 2 kg while trolling for largemouth bass (Wallis 1951). 73

Possibly they moved downstream into Lake Mead from the Colorado

River and its tributaries or from the Virgin River in Utah; rainbows are typically more migratory than most freshwater species, and tend to move downstream from planting sites. Creel data from NDW suggests that stocked rainbow trout disperse widely throughout the lake. Several obvious movement patterns are: (1) 25 percent of the plants in the upper Overton Arm displace to the lower lake, (2) Boulder Canyon plants show wide dispersal, and (3) spring plants move the furthest ; winter plants move the least.

Reproduction

Rainbow trout generally spawn from fall to spring depending on the characteristics of the water system. They are usually considered to be a spring spawner, although strains have been developed that will spawn at any time of the year (Lietritz 1959). Minckley and Carothers (1980) reported that trout reproduce from late fall to early spring (@ 7-12°C) in the

Colorado River in the Grand Canyon. During the fall run above Lee's Ferry in 1979, rainbow reached peak activity the third week in November at a water temperature of 11°C (McCall 1980).

Two males generally escort a single female to a gravel riffle where she selects an area and excavates a redd by sweeping the gravel downstream with her tail. The male does not assist with construction of the redd but usually stays close to the female courting her. Once complete, the redd may vary in diameter from 3 to 30 cm depending on the size the female and consistency of the substrate. The female then rests on the bottom of the redd with her mouth open which signals a male to move alongside with his mouth open. With a brief, quivering movement gametes are simultaneously released from bdth fish. The female immediately begins to cover the 74

fertilized eggs with gravel excavated from another redd upstream. The

spawning act may be repeated several times with 100-150 ova deposited at

each site.

Fecundity estimates range from 200 eggs per female to over 12,000

eggs. Most fish less than 30 cm TL produce less than 1,000 eggs. Selec-

tive breeding by fish culturalists has produced strains of rainbow that

are extremely fecund (Buss and McCreary 1960, Lewis 1944).

Eggs hatch within three to four weeks depending on water tempera-

ture. Survival of the developing larvae is positively correlated with

water flow and the concentration dissolved oxygen through the gravel (Coble

1961). A detailed description of the embryological development is des-

cribed by Knight (1963).

Successful spawning and recruitment of rainbow and other salmonids

in Lake Mead is very limited, if it exists at all. Gravid females were

observed by Jonez and Sumner (1954) along gravel shores; however, there were no young trout observed or collected. Several factors are involved, but

the obvious reason is the lack of suitable spawning habitat; there are no cold water tributaries flowing into the reservoir, other than the turbid

Colorado River. Rainbow trout attempt to spawn in the outflow stream of

the Lake Mead hatchery. Occasionally these fish are captured and stripped

for hatchery eggs (NFG 1976).

Rainbow trout successfully reproduce in Colorado River tributaries above Lake Mead; with the lower boundary appearing to be near Diamond

Creek (river mile 225.7). Rainbow trout fry (20 to 30 mm TL) were collected

in Diamond Creek above its confluence with the mainstream Colorado in

1976 by AGED and NDW. Trout may enter the Colorado during the winter 75 to spawn; however, the heavy silt load and associated high turbidity in the lower t.eaches of the river could deter such a movement. Spawning attempts by salmonids in the Colorado River immediately above Pierce Ferry would be futile due to the constant shifting of the sandy river channel which would rapidly suffocate any fertilized eggs.

Age and growth

Rainbow trout may live up to 11 years, but in the Southwest trout rarely live more than five or six years. Growth rates are highly variable, but are generally faster in large bodies of water with constant water temperatures. Stream populations are usually smaller fish depending on the numbers of fish inhabiting the stream and the degree of competition for space and food. Males may be mature at nine months (Van

Someren 1950) but most become ripe at age II (Hartman 1959). Females become gravid their third summer and most are fully mature by age IV

(Moore 1937). They typically grow faster and are longer lived than males.

In the Colorado River, rainbow trout show accelerated growth during the first year (157.4 mm) followed by a steady decline in annual growth increments (Carothers and Minckley 1980). Trout older than four years were collected but could not be aged from scale analysis due to irregular patterns of the circuli and extensive crossing over. In Lake Mead, growth is good to excellent depending largely on the age and size of the stocked trout, the season they are released and the stocking location. Creel data from marked fish shows an average growth of 1.6 cm per month (Roden

1979). The rapid growth may be attributed to the abundant threadfin shad. A study of rainbow in Shasta Lake, California, reports larger trout than in comparable lakes due to the abundance of shad (McAfee 1966). 76

Food habits

Trout are generally considered insectivorous feeding on both terrestrial and aquatic arthropods. The diet is very much dependent on availability of the food items and may include plankton, algae and fish. Rain- bow trout in lakes rely more heavily on fish than do stream populations that typically forage on drift organisms during the summer months and then shift to bottom invertebrates in the winter. In the Colorado River above Pierce Ferry trout have a variable diet; they consume at least

65 separate food items. Although there may be a wide spectrum of food items, Bryan and Larkin (1972) have found that individual trout have a specialized diet and generally do not utilize the entire range of foods.

The most common dietary component of Colorado River trout is the filamentous algae, Ctadophona gomeAata, followed by scuds. Based on the habitat characteristics of the invertebrate taxa ingested with the algae, it is presumed that both attached and drifting forms of Ctadophma are ingested (Carothers and Minckley 1980).

Prior to the introduction of shad in Lake Mead in 1954, rainbow consumed algae and zooplankton (Jonez and Sumner 1954). Once shad become established, they were extensively utilized by trout. Recent studies have shown shad as the dominant food. Chironomid larvae become more important during the winter and early spring when shad migrate to the lower levels of the lake (Deacon et al. 1972). The utilization of shad as the major food item is responsible for the excellent growth of rainbow trout (NFG 1965-1970).

Present status and significance to the fishery

Rainbow trout have been released in the reservoir yearly from 1959 77 to 1976 by the NDW. They were not taken in significant numbers until 1968 when an estimated 2,968 fish were harvested from the lower lake (NFG

1968). In the early 1970's, over 60,000 trout were harvested each year, representing about 13 percent of the total angling effort (Figure 2).

By 1975, an estimated 127,553 were harvested (19 percent of the angler effort) but the trout fishery drastically declined the following years; only 4,463 fish were taken in 1976 (1.0 percent of the angler effort) and 13,826 fish were taken in 1977 (2.4 percent of the angler effort) (NFG

1969 , 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977).

A follow-up study on the salmonid stocking program was initiated to determine spawning maturity, longevity and migration patterns. The Nevada stocking program was modified in 1977 to emphasize a "put-and-take" fishery with catchable trout. More trout were creeled in 1977 (Figure 2) but these fish averaged approximately 10 cm smaller than those taken in 1976. The greater number of smaller fish was partially related to the shift toward a

"put-and-take" fishery.

The total number of rainbow trout taken by anglers indicates since 1976 relatively poor survival of this species. NDW suggests several contributing factors: changing limnological characteristics of the reservoir, striped bass predation, and a loss of migrating fish up the Colorado River. The total number of trout lost from Lake Mead due to migration into the Grand

Canyon remains undetermined but is probably insignificant due to the turbidity gradient and absence of suitable foods.

•

25 130,000 120,000-

-- total number harvested 110,000 20 100,000_

percent of total catch — 90,000

80,000 — 15 =_ 3U@DIad

70,000

60,000- TU303

- S 50,000- 10 1. , LID3O0

30,000 - 20,000-

10,000 -

- 1—■ 1-4 c0 , VI VI ON ON ON CT CrN •■.1 --4 00 c0 • LA) 4*-• 00 0 rs..) LA) -P••

ON o

Figure 2. Estimates of total harvest and percent total catch of rainbow trout from Lake Mead, Arizona-Nevada, 1958-1977. 79

Carp

Carp are large-scaled fish with two barbels on each side of their sub-terminal mouths. Color varies from silver to gold or brown with red edges on their ventral fins. The generic name Coninto refers indirectly to the carp's fecundity derived from Cyprus the island home of Venus.

The history of carp introduction in the U. S. is interesting and tragic.

Originally native to Asia, carp were first brought to North America by

J. A. Poppe from Holstein, Germany, in 1872. Five of the 83 fish sur- vived the trip and were released in a private pond in Sonoma County,

California.

The editor of the August-September 1872 issue of the California

Mail Bag wrote concerning the debut of C. cavio to the western hemis- phere:

...The carp, to some palates, is one of the most delicious articles of food, and is more highly prized in Europe than other fish. It is like a delicacy on the table of the sub- ject and Emperor.

...In taste the flavor is even more delicate than of the finest brook trout (Lampman 1946).

In May, 1877, the United States Fish Commission imported its own brood carp from Germany warranting their introduction with the following criteria: fecund and adaptable to the process of artificial propagation, lives largely on a vegetable diet, hardy in all stages of growth, adaptable to conditions unfavorable to any equal palatable American fish and to very varied climates, grows rapidly, able to populate waters to their greatest extent, good table qualities and harmless in its relations to other fishes. The U. S. Legislature held the carp in such high regard that a law was passed imposing a $50 fine for destroying carp (Dymond 1955). 80

The true characteristics of the widely spreading immigrant began to surface in the 1890's as evidenced by a statement from T. Mills, Fish

Commissioner for the State of Nevada: "Several years ago, during the carp furor, the General Government, while not entirely to blame, was panticio ctimini4 in foistering upon this state and in polluting our waters with that undesirable fish." At that time Mr. Mills could not have fully realized the truth in his comment; today the carp is found throughout southern Canada, the continental U. S. and Mexico.

Distribution and abundance

Carp, Cypninws ea/L*0, were released into the waters of Nevada by

1881 when H. G. Parker, Fish Commissioner for the State of Nevada, stated:

Carp as a food fish, have no superior, when our streams are stocked with them the people of the state will possess as grand a luxury as found in the waters of those states celebrated for the abundance and variety of their fish; besides carp should be as plentiful to our people as chickens to the table of a prudent farmer...

The first record of carp in the Colorado River was in 1890 when they were reported as "a stranger in the Colorado River" (Gilbert and

Scofield 1898). This species and the channel catfish were apparently the only exotic species present along the lower Colorado River prior to the formation of Lake Mead. Both the "mirror" and "leather" varieties were commonly observed in the reservoir in the 1940's and 1950's. Carp were found along the littoral region, the pelagic area and in the rivers in 1954 and were collected at the surface and throughout the water column to a depth of 23 m (Jonez and Sumner 1954). Young carp were reported as abundant near the mouth of the Virgin River.

A total of 242 carp were collected during the investigation includ-

ing seven specimens of the mirror variety. There were no observations 81 or collections of the leather variety. Carp inhabit the entire Colorado

River and its reservoirs in Arizona. They were observed in the river and throughout the lake from Separation Rapids to Boulder Canyon. This species is second in abundance to threadfin shad in Lake Mead.

Reproduction

Carp usually spawn in the spring and summer at an optimum water temperature of about 18-20°C. In Lake Mead, there is always a segment of the population that is in spawning condition; gravid females and ripe males were collected throughout the year. Peak reproductive activity is in June. Large schools of carp move into shallow areas usually over mud bottom. Most spawning activities I observed were in the early morning usually one hour before sunrise. Usually, a single female escorted by three to ten males would swim close to shore where the female would dis- charge her eggs. The spawning ritual resulted in considerable splashing and often these fish would briefly find themselves high-grounded in the shallow water. During each spawning session approximately 300-500 fertilized ova would sink to the bottom and adhere to dead vegetation. A large female may release over 2,000,000 eggs per season. The eggs hatch is about five days (Struthers 1931, English 1952) and the larvae remain inactive until the yolk sac is consumed. In about one week the larvae are actively swimming and feeding on zooplankton.

Carp are extremely fecund, and a number of the Lake Mead population in reproductive condition year-around. However, based on the age class structure, carp reproduction and/or survival is not as successful as might be expected. This species has the greatest reproductive potential of the

Lake Mead fishes, but it is curious that there were no carp observed or 82

collected from the main reservoir younger than age class III.

Yearling carp were collected from Surprise Canyon and at the

mouth of the Moapa River which suggests these are warm water

nurseries. The apparent absence of juvenile carp from the main

reservoir is somewhat of a mystery. The age-class structure

suggest carp are able to successfully reproduce in the reservoir

at three to five year intervals. The factors governing this

cycle are not completely known but may be related to water level

fluctuations. The spring drawdown may be more detrimental to

carp than other species since carp deposit their eggs in water

less than one meter in depth. In more stable reservoirs carp

can successfully spawn in water only 7-10 cm in depth (Sigler

and Miller 1963).

Age and growth

Carp may grow to 40 kg but the largest taken from North

America is about 30 kg (Sigler and Miller 1963). In Arizona

waters carp weighing 13 kg have been caught (AGFD 1978); how-

ever, the average size about 2 to 3 kg. There are records of

carp living 47 years in captivity, although the maximum lon-

gevity in the Southwest is about 13-14 years. The oldest fish

collected in the Colorado River above Lake Mead was 12 years of

age (Carothers and Minckley 1980).

Growth during the first year is typically from 12 to 17 cm.

There is little difference in growth during the first year between reservoir and river populations in the Lake Mead National Recreation

Area. Carp from the Colorado River above Pierce Ferry grew 20.7 cm per 83 year compared to 21.6 cm per year for reservoir fish (Roden 1978, Minckley and Carothers 1980). There is a gradual decline in the annual growth increment for age class II to IV. After class IV there is little change in the growth pattern. The available data on sex differences in growth rates are inconclusive; several studies indicate there is no significant difference

(Sprague 1958, Nelson 1962) and others report females grow faster, particularly after the second year of life (Westman and Fahy 1940, Kessler 1961).

The average size of carp taken during this survey was 58.6 cm TL and 1.0 kg.

Condition factors ranged from 0.53 to 2.2 with an average of 1.34.

Food habits

Carp are omnivorous bottom feeders that utilize a wide spectrum of food items. They often forage for insect larvae by ingesting silt and extruding the debris to pick out food organisms from the water. Young- of-the-year fish are more selective feeding than adults foraging intensely on zooplankton. Young carp commonly consume eggs and larvae of their own species even when there is an abundance of plankton.

In the reservoir and the river above, algae is the dominant food.

Other foods consumed by the reservoir population include plankton, fish, fish eggs, inorganic rubble, and midge larvae (Jonez and Sumner 1954).

In the Colorado River, scuds and midge larvae are the most common invertebrates in the diet. Aquatic earthworms, blackfly larvae, and midge and blackfly pupae are also important food items (Minckley and Carothers

1980).

Present status and significance to the fishery

Lake Mead is another reminder of the notorious adaptability of the 84 carp. This species found the conditions favorable and spread extensively in Lake Mead and other Colorado River reservoirs. In fact, carp are ubiquitous throughout the entire Colorado River drainage.

This infamous species has a marked effect on the Lake Mead fishery.

At several locations where submersed aquatic vegetation was abundant, the destructive habits of carp were quite evident. Bare substrate was exposed in large areas where subaquatic plants that were providing cover and food for other fishes were uprooted and fragmented. This devastating impact on normal aquatic vegetation is well documented in the literature (Sharp 1942,

Black 1946, Chamberlain 1948, Threinen 1952, and others). Where carp were

"working", in protected coves and fingers, the water transparency would often be reduced from 10-12 m to 10-20 cm. The increased turbidity severely restricted light penetration to the remaining rooted plants; the eggs of largemouth bass and other species are covered by settling silt and suffocated.

Also, carp prey on the eggs and larvae of both crappie and largemouth bass.

Egg predation is documented by AGFD biologists who have observed carp consum-

ing eggs from centrarchid nests in Gregg Basin of Lake Mead (Brad Jacobson,

AGED, pers. comm.). The alteration and destruction of suitable spawning and foraging areas, combined with the predation of eggs and developing young,

is a serious detriment to the fishery.

Both Arizona and Nevada continue to permit fishermen to use carp as

bait fish in waters that are a common boundary. Attempts to commercially

harvest and reduce the carp population have not been successful. The irregular topography of the lake bottom restricts intensive seine collecting

and gill nets and other methods of collecting carp were curtailed when they

were found to be destructive to game fish species. The literature on carp 85

control is voluminous (Struthers 1929, Mottley 1938, Sigler

1955, Buck et al. 1960, and many others) but the methods are yet

unperfected. The carp population in Lake Mead will continue to

adversely affect the fishery until techniques are developed to

either harvest or selectively control carp without damaging other

species.

Red shiner

Red shiners, NotiLopiz tutAen4i4, are small minnows with

compressed bodies and terminal mouths. Breeding males are easily

identified when they become heavily tuberculated on the head and

all fins except the dorsal turn red or orange. The sides are

usually blue with a dark blue or purple crescent at the edges of

the opercles in breeding males. Non-breeding fish are silver

with white bellies and buff-colored backs. The specific name

tuttenziz means "otter" referring to Otter Creek, Arkansas, where

they were first collected. Now common in the Southwest, they are native to waters that drain into the Mississippi and Rio

Grande Rivers.

Distribution and abundance

Red shiners were probably first released into the lake as a "bait-bucket" introduction in the 1940's or early 1950's. In a letter to Carl Hubbs (December 11, 1954) Richard D. Boland stated, "I believe N. tutnen4i6 was first propagated at the

Arizona Fish Farms in 1948". The fish farm of which Mr. Boland speaks was Arizona Fish Farms, Inc., located at Ehrenberg,

Arizona. Apparently, the Arizona Fish Farm had constructed a 10 acre pond solely for the purpose of propagating red and golden shiners. 86

Red shiners were the most abundant species taken during the investigation; over 4,000 were collected. They are heavily concentrated in the warm turbid water near the mouths of the Virgin and Moapa Rivers but are rare along the shores of the reservoir. They also occur in the Colorado

River at Spencer and Surprise Canyons where other investigators have found them in large numbers (Deacon and Baker 1976, C. 0. Minckley, pers. comm.).

Reproduction

Red shiners spawn in streams and lakes preferring calm water over a gravel or boulder bottom. Shiners may deposit their eggs over plants, debris, or even centrarchid nests (Cross 1967; Minckley 1959, 1972). In reservoirs of central Arizona spawning usually takes place over sand or gravel beaches from March through June (Minckley 1973). They usually spawn in water ranging from 15-30°C, but are not restricted to a specific water temperature for spawning which permits a lengthy breeding season. A zig- zag chase usually precedes the spawning act, during which one or both fish may leave the water. The male stimulates the female to release her gametes by butting her with his tuberculated head. He uses his tubercles to assist in holding the female while she exudes her ova (Koehn 1965, Minckley 1972).

Red shiners hybridize with other members of Nutkop.i4 including N. ventotta (Hubbs and Strawn 1956), N.otitoptenws (Harlan and Speaker

1956), and N. tepiduis (Hubbs et al. 1953).

Age and growth

Red shiners mature their first year when they reach about 30-45 mm

TL. Growth during the following years ranges from 5 to 15 mm and they rarely exceed 80 mm TL. Maximum age is about three years. The red shiners collected from Lake Mead ranged from 11-74 mm TL. The average length was 59 mm. 87

Food habits

Morphologically, red shiners are best suited as plankti-

vores. They are very opportunistic feeders taking whatever organ-

isms are available at the time. Shiners forage in schools con-

suming surface and benthic insects, planktonic crustaceans and

algae. Most foraging occurs during the day with a peak in activ-

ity during the early morning hours (Hardwood 1972).

Present status and significance to the fishery

The red shiner is a fierce competitor. It has apparently

displaced the spikedace, Meda itugida, throughout its native range along the Verde River in Arizona (Minckley and Deacon 1968)

and a similar pattern is seen with another specialized native

minnow endemic to the Gila River Basin, the loach minnow, Tiatoga cobitis. In a Uescription of bait fishes used along the Colorado

River from Lake Mead to Yuma in 1952 (Miller 1952), the red shiner

was described as a questionable bait fish as it may be too small for largemouth bass bait. It was speculated that commercial propagation of this species as a bait fish would not lead to naturally reproducing populations along the Colorado River due to

the unsuitability of the habitat. Unfortunately, red shiners are well established in warm water tributaries of Lake Mead and the Colorado River because of fisherman releases and its aggres- sion and mobility. This species is legal bait fish in Lake Mead in both Arizona and Nevada and is common in bait shops near the reservoir. 88

Fathead minnow

Fathead minnows, Pimephata pkometuz, are small, robust fish with rounded fins, a blunt head and a relatively small, terminal, oblique mouth. The best distinguishing characteristic is the small, conspicuously crowded small scales anterior to the dorsal fin. They are generally olive- green dorsally and silver or silver-white on the sides and the ventrum is white or white-silver. Adults may have a dusky spot on each of the first two or three anterior dorsal rays and there may be a dark vertical bar at the base of the caudal fin. Breeding males become black or black-purple with two golden-copper bands that encircle the head and the anterior caudal peduncle. The snout and lower jaw become highly tuberculated and a spongy pad forms on the nape. Its scientific name is taken from the breeding males;

Pine-phata meaning fat helmet-ornament, and pkometu6, before black. Minckley

(1973) points out that P. p. coquato, a southwestern subspecies, is described from morphological characteristics that were later found to be clinal in nature (Tayler 1954, Bailey 1956).

Fatheads are native to southern Canada and the U. S. from the Rockies to the Appalachians and to the Rio Yaqui drainage in northern Mexico (Vander- merr 1966). Their range expanded as the bait industry prospered and they are now commonly found in ponds and streams in the Southwest. They adapt well to a variety of aquatic environments but are poor competitors. Fat- heads prefer quiet, muddy streams and are usually the first species to exploit intermittent waters and one of the last to succumb to drouth conditions

(Cross 1967). They are tolerant of a wide range of high temperatures, turbidity and alkalinity (McCarraher 1972) but tend to avoid strong currents and deep reservoirs. 89

Distribution and abundance

Carl Hubbs and Robert Miller examined specimens of the southwestern fathead minnow, P. p. conivauz (Girard), at Bob

Williams Bait Shop in Yuma, Arizona, on 23 March 1950. They were being propagated as a bait species but had not been used as bait in the river at that time (Evans and Douglas 1950). Today, the fathead minnow is a popular bait fish in both Arizona and Nevada.

They are frequently used to catch bass, crappie, and catfish in

Lake Mead.

. Fathead minnows are not established in the main reservoir.

They occur in Spencer Creek and Surprise Canyon above the reservoir (Deacon and Baker 1976, Suttkus et al. 1976) and at the mouth of the Moapa River (Deacon and Bradley 1972). Only seven fathead minnows were collected during this survey; six were from the mouth of Spencer Canyon and one was taken from lower Surprise

Canyon.

Reproduction

Spawning usually begins in the spring as water temperature nears 15°C and may continue into the summer months until temperature drops below 15.6-18.4°C (Prather 1957). The male selects a site underneath rocks, plants or debris in water less than one meter in depth. Typically, the undersides of stones are preferred to live or dead vegetation (Hasler et al. 1946). If the nest site does not meet his standards, he may improve it by smoothing and enlarging the hollow with the rugose pad on his nape.

A female then approaches the male, enticed by his courtship display, 90 and attaches her eggs to the underside of the object. The number of eggs produced by a single female may range from 636 (Isaak 1961) to over 2,600

(Carlson 1967). The size of the clutch is dependent on females that are courted by the male. Some nests contain as many as 12,000 eggs (Hodges and Ball 1953). The clutch is closely attended by the male who strokes the eggs with his dorsal pad to dislodge silt particles that might inhibit oxygen uptake (Wynn-Edwards 1932). The male is highly territorial, defending the clutch from other intruding males and his mate(s) who may consume her own eggs. The eggs hatch from four to six days at 25°C (Dobie et al. 1959) and the larvae emerge at about 4.8 mm TL. The young fish remain in or near the nest site for several days after hatching.

Hybrids are reported with the blunt nose minnow, P. notatto (Trautman

1957).

Age and growth

Fathead minnows usually die after about one year; a few may live to two or perhaps three years. Normally there is a heavy mortality of males after completion of the spawning act (Hubbs and Strawn 1956). During the first growing season, fish may reach 25 to 64 mm TL depending on water temperature, the abundance and availability of food, and the number of fish competing for the food items. Young fish may grow during the winter months even at relatively low temperatures of 2-7°C (Prather 1957). Some offspring of late spawns do not reach maturity until age class II and a few may live to three years. Those fish that reach their second summer are typically 80-85 mm TL.

Males are usually larger than females, often reaching a total length of over

100 mm (Carlander 1969).

Food habits

In situations where overcrowding is a problem, small invertebrates 91

or organic detritus may be consumed (Keast 1966); however, the relatively

long intestine and structure of the pharyngeal teeth indicate they are best equipped to consume and digest plant material. Typically, they are bottom browsers that rely mostly on diatoms and benthic algae (Coyle 1930,

Starrett 1950, Minckley 1963).

Present status and significance to the fishery

Fathead Minnows are not established in the main reservoir. They prefer the warm water of Spencer Creek and Surprise Canyon in the Lake Mead

Recreation Area (Deacon and Baker 1976, Suttkus et al. 1976) and the Lower Moapa

River (Deacon and Bradley 1972).

They are a relatively innocuous species and are considered excellent live bait by both fishermen and fish biologists (Evans and Douglas

1950, Miller 1952, Minckley 1969, Minckley 1973). This popular bait fish is sold from bait shops throughout Arizona and Nevada. I routinely checked bait shops near Kingman, Arizona, and Lake Mead during the summer of 1978 and found about 90 percent of fish sold that year were fathead minnows. If the states of Arizona and Nevada continue to allow the use of live bait fish in Lake Mead, this is one species that would be least harmful.

Channel catfish

Channel catfish, lc-tau/Luz punctatuz, are members of ictalurid fishes that are characterized by a well developed adipose fin, eight barbels

(two on the end of the maxillae, two on the snout, and four on the chin) and the absence of scales. The etymology of the scientific name is fish-cat

(Icta-tuhu4), obviously from the long catlike whiskers, and punctatto means

"spotted", derived from the irregular black spots along the sides. The spots are conspicuous in juveniles but tend to become less noticeable with age. 92

The head is compressed dorso-vertically with a terminal mouth with the upper jaw slightly longer than the lower jaw. The anal fin is relatively long and the caudal fin is deeply forked. The dorsum is green or gray becoming light gray or silver on the sides and the ventrum is white. Older fish and spawning males are typically more black or dark green.

The general body form of the catfish, which is characterized by a deeply forked tail, a flat head and streamlined body, suggests it is best adapted as a bottom-feeding inhabitant in large rivers or fast moving streams. Catfish are able to tolerate a wide range of temperatures, oxygen, turbidity and salinity and are found in a variety of aquatic habitats from warm water streams and stock ponds to clear, cold reservoirs.

The channel catfish is native to North America from southern

Manitoba to southern Quebec, west of the Appalachians to Florida and waters draining into the Gulf of Mexico (Eddy 1957, Trautman 1957). They were first stocked in California in 1874 (Shelby 1917) and in Utah in the late 1800's

(Sigler and Mitt- 1963). Their first appearance in Arizona was around

1892-1893 when the Arizona Fish Commission released 722 adults and yearlings in the Colorado River (Worth 1895). Another plant was made along the lower river in 1906 (Miller and Alcorn 1943). The catfish successfully established in the Colorado River and dominated the fishery before the river was impounded.

Distribution and abundance

Catfish were the most popular game fish in the Colorado River in

Arizona in the early 1900's. They quickly adapted to the cold water reservoirs behind hydroelectric dams and were abundant in Lake Mead in the 1940's (Moffett 1943, Wallis 1951) and the 1950's (Jonez and Sumner

1954). They were concentrated near river mouth areas, along old river 93 channels and in silt lined coves. The results of this survey show channel catfish are still common throughout the lake, but they are rare in the

Colorado River. Several adult fish (300-350 mm) were observed near the confluence of Spencer Creek and the Colorado River but there were none collected from the main river.

Jonez and Sumner (1954) tagged 89 channel catfish in the early 1950's with only two recaptures; one of the recaptured fish had moved only a short distance and the other was taken 8 km from the release point. The time span during which the movement took place was not indicated. The minimal movement displayed by one of the tagged fish was presumed due to the low water temperatures in the early spring when the study was conducted. The vertical migration begins in early October. They remain in the deep water until March or early April, when they can be seen near boulders or rock ledges.

Reproduction

Catfish spawning activity in Lake Mead was observed from May to

July. The peak activity occurred in June when water temperatures ranged from

20-29°C (Jonez and Sumner 1954). Gonadal somatic ratios support the earlier findings with the peak development of gonadal tissue from the second week of June to the middle of July. This is about three weeks later than the peak spawning period in most Arizona waters (Minckley 1973).

Typically, females produce about 1,500 eggs per kg until they attain a weight of about 9 kg and then the production of gonadal tissue increases to 2,000 ova per kg of body weight (Clemens and Sneed 1957). Fecundity estimates generally range from 2,000 to 70,000 ova per female (Katz 1954,

Migdalski 1955). Egg counts from Lake Mead channel catfish in 1954 re- 94 vealed the number of eggs per female ranged from 3,000 for a 30.5 cm fish to 5,500 for a 38.1 cm fish. Fecundity estimates for 13 catfish collected during this study range from 2,200 to 33,000 eggs per female. The average number of eggs per female was 10,930 for fish ranging from 260-550 mm TL

(Table 20).

In Lake Mead, eggs are laid under rock shelves or between large rocks at a depth of 2-10 m. The clutch is guarded by the male until the eggs hatch in about six to ten days. The male continues to protect the fry for one or two more days until they leave the nest site. Jonez and Sumner

(1954) stated that the fluctuation of water level in Lake Mead did not appear to have much influence upon successful spawning of catfish. This as- sumption is premature since there are no solid data on the influence if any, of fluctuating water levels on the reproduction of channel catfish in Lake Mead.

Age and growth

Age and growth of channel catfish are usually determined by analysis of pectoral spine annulii (Sneed 1951, Houser 1958) and in some cases, centra of vertebrae (Marzolf 1955). Although growth rates of channel catfish in Lake Mead are greater than those found from Lake Havasu, Arizona, they are about average for North American channel catfish (Carlander 1969).

In Lake Mead channel catfish grow about 15.2 cm (range 11.4-17.8 cm) the first year of life and 25.4 cm (range 20.3-30.5 cm) the second year (Roden

1978). Although there are no official records of the largest catfish taken from the lake, a 9 kg, 78.7 cm catfish, caught near Pierce Ferry in 1945, may be the record for Lake Mead (Wallis 1953).

Food habits

Channel catfish are more crepuscular than nocturnal; most foraging 95

Table 20. Fecundity estimates of 13 channel catfish from Lake Mead, Arizona-Nevada, 1978-1979.

Total len th mm No. ova

260 2,200

265 2,100

289 2,500

340 3,400

342 3,100

360 4,200

394 8,100

405 7,400

407 7,400

492 19,400

507 28,200

515 27,000

550 33,000 96 of tagged fish in a northern Arizona reservoir occurs during the dark hours before dawn and at dusk (McCall, unpubl. data). Bottom arthropOds are usually preferred until the fish reach a total length of about 100 mm when they shift to a piscivorous diet. Before shad were established in the reservoir, the most important foods for Lake Mead channel catfish were algae and fish, including young bass, crappie, sunfish, and other catfish.

Food habit analysis during this study revealed that crayfish and threadfin shadare the dominant foods. These data are compared to diet studies of channel catfish in 1972 in Table 21. The results are similar except for the recent utilization of crayfish, P. eta/L.12,i, as a food item. Generally, catfish prefer crayfish over other food items including bluegill and green sunfish (Lewis et al. 1965). The relatively high incidence of P. ctanki in catfish stomachs suggests crayfish may be present in greater numbers on

Lake Mead than in the past.

Present status and significance to the fishery

A study in the early 1950's indicated that the catfish was an important game fish, second only to largemouth bass (Jonez and Sumner 1954).

Although they have not been stocked in the reservoir, creel information indicates the population is stable or perhaps increasing. Many catfish in a range of age classes were observed during electrofishing activities.

The channel catfish often does not receive the attention that has been given the legendary largemouth bass and its rival, the striped bass, but the importance of the catfish to the Lake Mead fishery should not be underestimated. A summary of creel census results shows that the number of catfish harvested from the lake has consistently been over 30,000 fish per year, and since 1967 the number of fish harvested annually has not Table 21. Food habits of channel catfish from Lake Mead, Arizona-Nevada.

Deacon et al. 1972 McCall 1978-1979 (n=63) Percent frequency occurrence Frequency of Percent Food item Oct. 21 May 4 June 9 Food item occurrence frequency occurrence,

Threadfin shad 33 25 empty 20 32

Chronomidae 19 75 2 plant remains 14 22 Odonata 1 Crayfish 7 11 Pnocambau4 ctakkii Col eoptera 5 Threadfin shad 7 11 fish remains 38 Odonata 4 6 plant remains 42 1 Anisoptera (3) Zygoptera (1)

Chironomidae 4 6

Bluegill 2 3

Col eoptera 2 3 Dytiscidae

zooplankton 3

fish eggs 1 2 g8

fallen below 10C11000. The greatest number of channel catfish caught in a

single year was in 1963 when over 200,000 fish were taken. In 1977,

they replaced largemouth bass as the most important game species when over

170,000 were taken; this represented 30 percent of the total catch. The

largemouth bass remained the most popular species with about one-third of the total angling effort but creel data indicates a trend in the number

of anglers fishing for the channel catfish. The number of catfish anglers has almost doubled from 3.5 percent in 1975 to 5.9 percent in 1977 (NFG

1975, 1976, 1977). A summarization of total harvest and percent total catch data from NDW creel records from 1958 to 1977 is shown in Figure 3.

The channel catfish has been, and remains today, one of the most popular fish in Lake Mead and the Southwest. The eurythermal character-

istics of this fish make is especially adaptable to the relatively warm streams and ponds of Arizona and Nevada and the adjacent cold water of the Colorado River reservoirs. Its popularity lies partially with the fact that catfishing does not require a large dollar investment in fishing gear commonly purchased to stalk the largemouth and striped bass in Lake

Mead. The table qualities and large size of channel catfish have earned this species the respect of anglers, not only in Lake Mead but throughout the

United States.

Yellow bullhead

The yellow bullhead, Ictatunu4 nataLbs, is the most heavily bodied of the catfishes as suggested by their specific name natal's, meaning

"having large buttocks". The original name was from the stocky, obese specimens described by LeSueur in 1819. In other waters their color may 200,000 30

175,000 1 /1 1 / I \ 25 , \ , \ i 150,000 , I \ \ / I \

I 125,000 20

V /

100,000 N/

15 lUa310d \

75,000 L1J1VJ total number harvested 10

50,000 Percent of total catch

5 25,000

0-• ■-• I-. ■-•• k---, ■-+ , 4 4 i- ■-■ 1 1 1 4 1 4 1 4 4 4 , _ /0 /0 1/40 /.0 /0 / 0 1/0 1/40 1/.0 1/4.0 ./0 1/40 %.0 %. 14 14 14 14 4 4 4 0 0/ 0/ 0/ 0/ 01/ 01/ 01/ J V V V -V V -.4 CO \.0 0 (...) CN V Co 1/40 0 ln Lil as 'V 1.0 Year 4.0 0 Figure 3. Estimates of total harvest and percent total catch of channel catfish from Lake Mead, Arizona-Nevada, 1958-1977. 100

vary from yellow s brown or dark brown, but the specimens I examined are easily identified in the field from the brown and black bullhead by the bright yellow color. Yellow bullheads from the Lake Mead Recreation

Area are almost a lemon-yellow color along the dorsum and sides and shade to white along the ventral surface. Chin barbels are white and there is no evidence of mottling that sometimes occurs in the other Arizona bullheads.

Its native range is most of the United States east of the Rocky

Mountains and it is curious that they are not more common in the southwest U.S. Apparently, the yellow bullhead is not abundant in Utah and

Nevada and is rare in California (Moyle 1976). They are common Arizona waters but are relatively obscure in scientific collections (Minckley 1973).

Distribution and abundance

To the best of my knowledge, there are no records of yellow bullhead in the Colorado River in Arizona above Hoover Dam. They do not inhabit Lake Mead or the Colorado River in the Grand Canyon but have found a refugium, where they occur in small numbers, in the relatively warm backwaters of Emory Falls Canyon and Green Rock backwater. A total of 12 adult fish were collected from these areas during the winter of 1978. One unidentified bullhead was observed but not collected at the mouth of Spencer

Creek in December 1978.

Reproduction

There is little information available on the biology of yellow bullhead in Arizona. The spawning behavior, breeding age, and time of year are similar to the black and brown bullhead (Breder and Rosen 1966).

Spawning typically takes place in the spring from May to June when the 101 female constructs a shallow nest with her tail. The male and female posi- tion themselves head to tail and the female releases her eggs. After the male fertilizes the eggs, the clutch forms into a yellow sphere that is guarded by one or both parents until the larvae hatch and disperse.

Age and growth

Yellow bullhead may live to an age of five years. The fastest growth is during the first two years when growth increments are about 60 and 85 mm, respectively. Subsequent growth is about 50 mm per annum.

Maximum length is 45 to 50 cm and maximum weight is about 1 kg. (Schoffman

1955). The yellow bullhead collected during this survey were 192 to 242 mm TL

(average 236.7 mm) in length and weighed from 125 to 255 grams (average

217.2). The mean condition factor for the twelve specimens was 1.62.

Food habits

The yellow bullhead is more picivorous than the brown and black bullheads. They consume fish (McClellan 1954, Minckley 1973), mollusks, aquatic insects and crustaceans (Flemer and Woolcott 1966, Miller 1966).

The winter foods of the specimens examined from the Colorado River contained snails (49% by volume), algae (13%), chironomid larvae ( 1%) and detritus (37%).

Present status and significance to the fishery

This is a fine flavored fish that may weight over 1 kg in Arizona

(Minckley 1973); however, they are quite rare in Lake Mead and contribute little to the fishery. Because it tends to grow larger than the other bullhead species and is taken easily with live or prepared bait, it is a potentially valuable game species. Both the yellow and black bullheads occur within the Lake Mead Recreation Area but the yellow bullhead is 102 seldom found in the turbid, quiet waters that is normally inhabited by the black bullhead. In some streams and rivers, particularly where siltation has increased, the black bullhead has the potential to displace the yellow bullhead (Clay 1975). It is doubtful that both the black and yellow bullhead will be sympatric in the Colorado River or its reservoirs since they are usually segregated by preference of habitat and rarely coexist.

Black bullhead

The black bullhead, Ictaunlus metaz, is one of the smaller bullheads that can be differentiated from T. nebuto4,bs by short, broad head and stubby straight pectoral spines with only rudimentary serrae at the posterior edge. The jaws are nearly equal length with pigmented chin barbels.

The name metco, meaning black, appropriately describes young fish that are typically jet black with grey or mottled bellies. Adults may vary in color from yellow to brown or black. The single speciman collected from Lake

Mead in 1979 was a dark brown color shading to yellow-grey on the ventrum.

At the base of the caudal fin was a distinctive pale vertical bar.

The black bullhead is native east of the Rocky Mountains from Montana to western New York, and south to Alabama and Texas. Its native range does not extend into Arizona but reaches to the northeastern corner of New

Mexico (Koster 1957). Now widespread, it can be found throughout the continental United States. Preferred habitat is usually warm, turbid ponds and lakes over mud bottoms, and occasionally stream pools and river backwaters.

This was one of the first introduced species in California in 1874

(Curtis 1949) and one of the early exotics to become established in west- central Nevada (LaRivers 1962). Likely they found their way to the Colorado 105

minnow" is inspired from the numerous vertical bars along the sides. These

dark bars usually number between 14 and 18 and are typically wider in males.

The preferred habitat is shallow, open areas of streams and rivers, usually

over a sand bottom. Killifish can be found in springs and seeps and are

able to tolerate relatively high concentrations of alkalinity and salinity.

The Rio Grande killifish is native to the Brazos Colorado, Pecos

and Rio Grande Rivers in Texas and New Mexico (Moore 1968) and the salty

pools on the Llano Estacado of northwestern Texas (Sigler and Miller 1963).

Its present distribution includes the lower tributaries of the San Juan and

Colorado Rivers in Utah (Sigler and Miller 1963) and it has been collected in San Juan and Kane counties in southern Utah in the 1950's. This unique fish was present in the Little Colorado River in Arizona prior to 1938

(Miller and Lowe 1967) and has remained locally abundant throughout the state. Killifish were collected by AGFD biologists in the Colorado River below the newly completed Glen Canyon Dam (Stone 1964, 1965) but they soon disappeared due to the cold water released through the dam.

Distribution and abundance

Rio Grande killifish were found in bait tanks along the Colorado

River below Lake Mead in 1950 (Miller 1952). They inhabit the mouths of

Colorado River tributaries through the Grand Canyon National Park (Minckley and Blinn 1975, Deacon and Baker 1976, Suttkus et al. 1976, Carothers and

Minckley 1980). This species was most recently collected at the mouth of

Spencer Creek in August and December 1978. They were also seined from a backwater at the mouth of Tincanebitts Canyon (river mile 263.7) in October

1978. To the best of my knowledge, killifish do not occur in the main reservoir and have not been collected in the Colorado River in the Lake

Mead Recreation Area below Tincanebitts Canyon. 106

Reproduction

Spawning in Arizona waters occurs from April to May (Minckley 1973).

There is little other information available on the reproduction or, in

fact, the life history of this species. The biology of the Rio Grande killi-

fish is probably quite similar to that of a close relative, the plains killi-

fish, F. kan4ae, which is discussed in detail by Minchley and Klassen (1969a,

1968b) and others (Simon 1946, Koster 1948, Cross 1958).

Food habits

The principal foods of the members of the genus Fundutu4 are surface

insects and plankton. In the tributaries of the Colorado River, food items

of the Rio Grande killifish consist of a variety of both bottom-dwelling and

floating aquatic insects, particularly chironomids and ephemeropterans

(Wilde 1976).

Present status and significance to the fishery

Rio Grande killifish are a rare, relatively innocuous species found

only from Spencer Creek and Surprise Canyon in the Lake Mead Recreation Area.

They were reported from bait tanks along the Lower Colorado River below

Lake Mead in 1950 (Miller 1952) and may occasionally find their way into

bait shops near the reservoir though I have not observed them. They are

not important to the fishery and it is doubtful there will be any change in

their present status, at least in the foreseeable future.

Mosquitofish

The mosquitofish, Gambusia a64in4.4 aWniz, is a viviparous topminnow

characterized by a stout body, short flat head and small oblique

mouth with the lower faw projecting above the upper. It is native to the

eastern United States from southern Indiana and Illinois to the Gulf of 107

Mexico and north along the Atlantic Coast to New Jersey. Because mosquito

larvae are one of their favorite prey and because they are known to reduce

adult mosquito populations in some cases, this fish was enthusiastically

released in North America and other continents during the 1920's. In many

cases they were used not only for pest control, but also to help prevent

malaria. Able to withstand a variety of environmental conditions, they quickly

became established in the warm climates over most of the earth. Today,

the mosquitofish is probably the most widely distributed fresh water fish

in the world.

Mosquitofish rapidly gained pcp:Ilarity and were brought to California

in 1922 to control the pestiferous mosquito. They quickly made their way

eastward into Nevada. The first documented releases in Nevada were from

the Los Angeles vicinity into the lower Carson River in 1934 (LaRivers 1962),

although they were probably in Nevada, at least along the western border,

prior to 1930. Originally stocked in the state of Utah from Tennessee in

1931 (Rees 1934), they are now locally abundant in warm Utah waters (Smith et al. 1959).

The earliest record of this species in Arizona is 1926 (Miller and

Lowe 1967). Today, they have spread throughout the state occurring in a

variety of habitats including stagnant stock tanks, clear, warm water springs, and the shallow areas along the shores of large reservoirs.

Distribution and abundance

They were able to survive the vagaries in the Colorado River above

Lake Mead for two years after the closing of Glen Canyon Dam in 1964 (Stone

1964, 1965), but, as with the other warm water species inhabiting the river, the drastic decline in water temperature curtailed successful re- 108 production which resulted in the eventual extirpation in the main river from Glen Canyon Dam to Pierce Ferry. In Lake Mead, earlier collectors have found them at Emory Falls and Pierce Ferry (Deacon and Baker 1976,

Suttkus et al. 1976), in shallow protected areas along the shore of the main reservoir (Moffett 1941, LaRivers 1952, Jonez and Sumner 1954, Miller and Lowe 1964) and at the mouth of the Moapa River (Miller and Alcorn 1946).

A total of 1,329 mosquitofish were seined during the 1978-1979 survey. They were the third most abundant species in seine collections (0.21 2 fish/m ). Mosquitofish were taken throughout the study area in the

Colorado River (river mile 248.5, 267.5, 273.1), Grand Wash, God's Pocket,

Gregg Basin, Bradley Bay, Granite Cove, Temple Basin, "Burton's Finger #1", and were abundant near the mouths of the Virgin and Moapa Rivers. Although mosquitofish were not collected from Virgin Basin, there is no reason to suggest they do not occur there in isolated populations.

Reproduction

Mosquitofish are members of the family Poeciliidae, a group of fishes that bear living young. The sexes are dimorphic. The smaller male develops an elongated gonopodium from the third, fourth, and fifth anal rays.

Rather than broadcasting the eggs and sperm, fertilization is internal.

The intricate behavioral patterns associated with courtship rituals and copulation are described in detail by Itzkowitz (1971) and Peden (1972).

Under optimum conditions females are capable of producing at least four broods of young per season (Moyle 1976), with a maximum of about five broods per lifetime. The number of embryos per female varies greatly, ranging from a few individuals to over 300 (Krumholf 1948). Usually, the average size of the brood is 40-100 young (Smith 1912, Kuntz 1914, Hildebrand 109

1917). Most adults die their first summer, although some may live two

years. The older fish are typically females which are physiologically

hardier. Although they are short-lived and produce relatively few off-

spring, the reproductive strategy of nuturing the young and bearing them

alive greatly reduces initial mortality that occurs with most egg-laying

fishes.

Age and growth

Growth of male fish apparently stops at about 30 mm TL when the

gonopodium is formed. The females may reach up to 50 mm TL depending on

the productivity and temperature of the water. Most fish die at one year

but a few may live to 15 months (Krumholz 1948, Goodyear et al. 1972).

Food habits

As expected, mosquitofish show a preference for mosquito larvae and

pupae. They do not necessarily feed selectively but are opportunists that

consume zooplankton, algae and even small fish (Barnickol 1941, Harrington

and Harrington 1961). In situations where animal foods are scarce, mosquito-

fish may feed exclusively on filamentous algae and diatoms (Rees 1958).

Present status and significance to the fishery

The sale and use of mosquitofish as a baitfish in Lake Mead is per-

mitted by both Arizona and Nevada (AGED 1979 , NDW 1979). Any use of these

species as bait would presumably be limited to late summer when the females

read the size preferred by bait fishermen. Since I have not found them in

bait shops in Arizona nor have I observed them being used by Lake Mead

anglers, their commercial value as baitfish is probably minimal.

Their usefulness as a mosquito control agent has been of special importance in recent years due to their ability to develop resistances to 110 pesticides. They can be released in areas to complement chemical control agents (Rosato and Ferguson 1968) and in some situations mosquitofish introductions have replaced the use of pesticides. In the Central Valley rice field in California, the mosquitofish was found to be more effective and less costly than pesticides (Hoy et al. 1972). It is unfortunate that their talents in reducing mosquito populations are of little value in Lake

Mead since mosquitoes have not been a major problem.

Although mosquitofish have the potential of being an abundant forage fish, food habit analysis of Lake Mead fishes indicates they are seldom utilized. One reason may be that in areas where they are abundant they are not available to the predators. Mosquitofish are found in shallow (/-15 cm), protected, warm water "thermals" immediately adjacent to the shore where water temperature ranges from 3-7°C higher than the average surface temperature of the reservoir. Even when disturbed, they are very reluctant to venture out into the cooler water where they would be easy prey.

In Lake Mead, where there is an exiguous macroinvertebrate community, any further cropping of that critical trophic tier by a voracious predator such as the mosquitofish would be a detriment to the survival and recruitment of other species. The skill of mosquitofish in out-competing other fishes, particularly native forms in undisturbed areas, is well-documented

(Everman and Clark 1931, Miller 1961, Myers 1965, Minckley and Deacon 1968,

Minckley 1973, and others). They also have the capability to influence the population size of other fish species, including largemouth bass, by predation of the young (Myers 1965). They should remain only locally abundant in Lake Mead at the present temperature regime. 111

Striped bass

The striped bass, Mmone Aaxatituis, is one of four species of the family Percichthyidae (temperate basses) found in North America. It is distinguished by separate spiny and soft-rayed dorsal fins, six to nine black horizontal stripes on the sides, and a small gill (pseudo-branchia) inside each gill cover. Stripers have large, oblique mouths with the lower jaw projecting over the upper. Color varies from silver to bluish- black on the dorsum and silver to white on the belly. Lake Mead stripers are metal grey to olive-green along the dorsum shading to silver or silver- white on the sides and white along the ventral surface.

The generic name for the striped bass has changed back and forth between Amone and Roccuz over the years. AFS now recognizes the striped bass and the three other American basses under the genus Moune. The specific epithet 4axatitta means "living among rocks" which seems rather inappropriate for a fish that is commonly found in the pelagic regions of inland reservoirs. The term is probably derived from the old common name "rockfish".

The striped bass was once celebrated as a large anadromous fish that seasonally entered the rivers and estuaries of the Atlantic and Gulf

Coasts where it is native. This species was first introduced along the west coast of the United States in 1879. Within a few year, stripers weighing 17 pounds were caught which prompted an ordinance that prohibited taking stripers under eight pounds. They adapted well along the Pacific drainage and reproducing populations are now found from southern California to Washington (Raney 1952).

A landlocked population was reported in 1954 from newly constructed 112

Santee-Cooper Reservoir in South Carolina (Stevens 1958). By 1959, stripers made up 40 percent of the total catch of all species from that reservoir system. It was apparent that if a suitable forage base was present and

spawning requirements were met, striped bass would reproduce in fresh

water. Breeding populations of stripers first appeared in the Kerr Reser-

voir on the North Carolina-Virginia border and on the west coast in Miller-

ton Lake, Calif. The success of striped bass in fresh water lakes and reservoirs is reviewed and discussed by many authors, notably Barkull (1967),

Bayless (1967), Bishop (1967), Goodson (1966), Stevens (1969), Ware (1970) and Erickson et al. (1971).

At first, attempts to raise stripers in hatcheries was not successful and very few viable fry were produced. Eventually, a catheter sampling technique was developed to determine when the female was entering her critical 60-minute post-ovulation period. Nearly 150 million striped bass fry were produced with this method from a single hatchery at Mericks Corner,

South Carolina from 1964 to 1968. The demand for striped bass grew rapidly, not only from numerous state and federal agencies, but also foreign governments such as South Africa and the Soviet Union. In 1968, over 150 million striped bass fry were reared from only three eastern hatcheries in North and

South Carolina and Virginia. These long-lived fish became popular very quickly and were released in reservoirs along the east coast,in the Mid- west, and eventually in the Southwest.

Distribution and abundance

Striped bass were first stocked in the lower Colorado River in Arizona in 1959 (St. Amant 1959) and in Lake Mead in 1969. During a four year period from 1969 to 1972, over 65,000 fish were released into Lake Mead 113

(Table 22). Successful reproduction was first documented in the reservoir

in 1973; an event which gave birth, in my opinion, to one of the best striped

bass fisheries in the United States.

During this survey, striped bass were frequently observed in the

main lake and only occasionally in the mainstream Colorado River. Their

pelagic habits and cunning mastery in avoiding trammel nets made collecting

difficult. Most stripers taken in open water were caught with fine strand

experimental gill nets, but the small mesh size of these nets restricted

the catch to fish less than 4 kg. Electrofishing was successful for striped

bass during the summer months when schools of two to six fish enter the

shallow water to forage on threadfin shad and crayfish. Young-of-the-year

and yearling stripers were commonly seen in shallow water along the shore

but were consistently able to evade and resist electrofishing attempts.

Reproduction

Optimum conditions for spawning in Lake Havasu, on the Colorado River, occurs from early April to mid-June (Edwards 1974). The peak spawning activity in upper Lake Mead is from April through early July. Spawning may occur at any time during the day but usually takes place in late after- nor or early evening (Calhoun 1976). Males first begin to congregate near the surface in small groups. The female arrives, escorted by several males, and the school moves in a circular pattern, turning on their sides and splashing water. The ritual lasts only about a minute and then the fish disperse (Morgan and Gerlach 1970, Raney 1952). Spawning activity usually o begins as the water temperature approaches 14 C and terminates when the temperatures reaches 20°C (Raney 1958, Goodson 1966, Talbot 1966). In areas where a shallow thermocline exists, violent storms may suddenly cause an upwelling of cold water which may destroy fertilized eggs if water temperature falls below 13°C (Albrecht 1964).

114

Table 22. Summary of striped bass stocking records in Lake Mead, Arizona-Nevada.

Year Number released Ave. size (cm)

1969 20,000 5.1 - 7.6 (2-3")

1970 41,300 5.1 - 15.2 (2-6")

1971 910 20.3 (8")

1972 3,000 15.2 - 20.3 (6-8") 115

Female striped bass are extremely prolific and may produce as many as four million ova in one season (Jackson and Tilles 1952). Egg production is typically 176,400 mature ova per kilogram of body weight (Lewis and

Bonner 1966). The eggs are slightly heavier than fresh water and will slowly sink to the bottom and usually suffocate if not kept in suspension.

In certain situations striper eggs may sink to the bottom and survive, but generally the eggs suffocate either by siltation or bacterial respiration at the bottom interface. If conditions are suitable, the eggs will hatch in about two days and the larvae will drift for another week until they begin swimming and feeding on zooplankters.

Assuming striped bass in Lake Mead seek areas of moving water to spawn, the most suitable areas for striper reproduction are below the Colorado River near

Pierce Ferry and the Grand Wash-Iceberg Canyon area. It is in this vicinity of the upper lake that numerous adult fish are observed dead or dying each spring. Moribund stripers are reported throughout the lake in the spring and in the Colorado River as far as Surprise Canyon, but most are concentrated in the upper lake near Pierce Ferry. Dying fish become disoriented and usually swim counter-clockwise in small circles, with the head bobbing above the surface. Tissue samples of moribund fish have been analyzed by the USFW's Fish Cultural Development Center in Bozeman, Montana, with the following results.

.... degenerative changes in kidney tubules and arterioles liver. Tubules epithelial cells showed hydropic degeneration and swelling. Arterioles in liver sections showed arterio- sclerosis in which the wall of the arteriole was thickened resulting in a reduction in the diameter of the lumen.

I suspect that the high mortality may be due to the stress of spawning perhaps coupled with some other stress, such as environmental, etc. (Charlie E. Smith, Sept. 1978). 116

Recently, several questions have arisen concerning the future of striper fishery and the potential impact of migrating fish to the salmonid fishery and the endangered humpback chub above the reservoir. A close examination of the habitat above Pierce Ferry reveals several factors that make the mainstream Colorado River less than optimum for successful reproduction or migration of striped bass. First, as the Colorado River flows through the Grand Canyon it picks up a tremendous silt load that is deposited in the pierce Ferry area; secchi disc readings are often less than

15 cm in this area of the lake. Since the bass is a sight feeder, the turbid waters of the Colorado River severely limits the foraging efficiency.

Second, forage fish are scarce in the river. Threadfin shad are not found above Pierce Ferry in any numbers as the water temperature is below the thermal tolerance of the shad and there is not an adequate zooplankton population to support them. The few carp and suckers that inhabit the lower portion of the river are generally too large to be prey for striped bass less than 15 kg. Last, if stripers were'able to spawn in the river, water temperatures in the Colorado River are at the low tolerance limit for successful survival of the eggs (Turner 1962, Albrecht 1964).

In short, factors that may be acting to limit the expansion of the striped bass into the Colorado River above Lake Mead are: (1) absence of a suitable food base, (2) reduced foraging in turbid water, and (3) water temperatures that prohibit normal fertilization of eggs.

Age and growth

Striped bass are a long-lived fish often reaching 30 years of age and weighing 56 kg. Stripers from land-locked poOulations seem to grow faster than anadromous fish but are not as large and rarely reach over 30 kg.

Growth is usually the fastest during the first four years; after this time 117

the female matures and usually grows faster and lives longer than males.

Some males may spawn at the end of their first year but most males mature

at the age two or three years.

Striped bass that were first stocked in the Colorado River reservoirs

grew 152 mm TL their first year in Lake Havasu (Edwards 1974) and 146 mm

TL in Lake Mead (Johnson and Roden 1977). The offspring of these fish grew

an average 55 mm more than their parents in Lake Havasu and 50 mm more in

Lake Mead. By age class V, the growth patterns of hatchery-reared stripers

was nearly identical to that of "wild" fish. The differences in initial

growth is related to the physical stress of the hatchery conditions and the

subsequent adjustment to the "wild" environment. The annual growth of

three yearling fish I examined from Lake Mead was 247, 255 and 258 mm TL

which is similar but slightly greater than results of Roden and Johnson

(246 mm IL) and slightly less than that reported from stripers collected

in the Colorado River above Pierce Ferry. First year growth of several

specimens from the Colorado River was from 260-270 mm TL (C. 0. Minckley,

MNA, pers. comm.). Annual growth increments steadily decline after the first

year. Roden and Johnson (1977) found growth rates of 24.4, 15, 7.9, and

5.0 cm for age classes II through V.

The size of stripers collected during this survey ranged from a 103-

540 mm TL. Condition factors ranged from 0.73 to 1,31 with an average of 1.00.

Food habits

Young-of-the-year fish (5-18 cm) rely almost exclusively on zoo— plankton. This diet of yearling fish seems to remain unchanged until the early fall when shad fry are quite abundant. Subadult bass (28-50 cm) are opportunistic piscivores that show a marked preference for threadfin shad.

They may continue to utilize invertebrates if forage fish are scarce. 118

Adult striped bass are gregarious, voracious predators that effectively utilize threadfin shad in Lake Mead. They apparently take advantage of fish stocking efforts as an angler recently found nine largemouth bass reward tags in the stomach of an adult striper a few days after the largemouth were stocked (Wes Martin, AGFD, pers. comm.). Johnson (1976) analyzed stomach contents of 112 bass in 1976 and found a high incidence of rainbow trout. The stripers were collected within just a few days of a trout release.

They are opportunists taking relatively large numbers of crayfish during the summer months (Table 23). The relatively high occurrence of crayfish (11%) in striper stomachs shows a dietary shift occurring from

June to late August when the bass follow schools of shad into the littoral zone. Similar dietary shifts to insects and to other fish species, such as crappie have been documented (Stevens 1958; Domrose 1963). The stomach of a 28.4 kg striper taken just above Separation Rapids in 1979 contained a single anal spine from a carp (C.O. Minckley, MNA, pers. comm.), which indicates they are able to shift to non-preferred forage fish when they migrate into the Colorado River in the spring. Similar shifts in diet of striped bass are not uncommon and are usually associated with a decline in the numbers of clupeid fish.

Present status and significance to the fishery

Although the striped bass is a relatively recent immigrant to inland waters of the United States, this species has proved its potential as a prized sport fish (Ramey 1952, Skinner 1962, Talbot 1966,

Turner and Kelly 1966, Goodson 1966, Turner 1972, Edwards 1974). Some avid largemouth bass fishermen still find it hard to accept the striper as quality sport fish, perhaps because many are unaccustomed to the tactics of striper fishing. Many are quickly being converted when they 119

Table 23. Stomach contents of striped bass from Lake Mead, Arizona-Nevada.

Johnson 1976

Frequency of Percent Food Item occurrence occurrence threadfin shad 56 50 empty 28 25 rainbow trout 26 23 debris 7 6 crayfish 4 4 chi ronomids 1 1 golden shiner 1 1 black crappie 1 1

McCall 1978-79 empty 14 39 threadfin shad 11 30 zooplankton 6 17 crayfish 4 11 largemouth bass 1 0.03 120

catch fish that often weigh over 9 kg.

Striped bass first began to show up in the creel in Lake Mead in

1971 and 1972, and catches have increased each year. In 1977, NDW esti-

mates 13,250 fish were harvested, representing 2.3 percent of the

total catch (Figure 4). The most significant trend illustrating rapidly

growing popularity of the striper is the angler preference data shows that in

1975 only 2.3 percent of the Lake Mead anglers were fishing for striped

bass and by 1977 this figure increased to 11.3 percent (NOW 1975, 1976,

1977). The increased harvest of the striped bass, in recent years, has

been partially due to well-educated anglers who have perfected strategies

to exploit the open water habits of this species. Also, commercial

development of sophisticated sonar location devices and deep water

trolling equipment has allowed the striper fishermen to effectively har-

vest fish from Lake Mead and other deep reservoirs.

The size and numbers of striped bass in Lake Mead steadily increased each year convincing biologists from Nevada and Arizona to lift the 16

inch minimum size restriction from Lake Mead in 1977, but the story of the striped bass in Lake Mead is by no means complete. The population dynamics

of this species in Lake Mead, and other reservoirs of the Colorado River

is not known. Studies of other reservoirs have indicated that stripers

will increase in numbers, creating excellent fisheries, until they reach

a point where they exceed the available food and space and then a die-off

occurs. The phenomenon, as it applies to reservoirs along the Colorado

River, has been addressed by W. L. Minckley:

Management of the lower Colorado River ... (it) most illogical in light of most information available in fisheries management, and more importantly, perhaps, in basic biology ... The food base is simply narrow, and little latitude is available from an over-all shift in the trophic economy of these waters ... Striped bass populations are voracious Figure PALSANIUG IAQTUNU TULOJ, 15,000 10,000 5,000 4.

1970-1977. Estimated totalharvest percent totalcatch total numberharvested and totalcatchofstriped bassfromLakeMead,Arizona-Nevada, 1-■ N.)

oso"

- 3.5 - 3.0 1.5 1-0 2.0 2.5

LPLUD TVIO4 LUAOLED

122

predators, quite capable of substantially reducing the population of its prey species ... In Santee-Cooper Reservoir, the (striper) population expanded rapidly after about 1950, utilizing clupeid fishes as forage base, and the population peaked about 1969, then declined 30 to 40 percent (Stevens 1958, 1964) since the forage populations had been reduced to an extent beyond its capacity to support the predators ... In short, if striped bass undergo a successful "population explosion" in the reservoirs that have substantial stretches of flowing stream above them, such as Lake Mead, a remarkable fishery may develop for a time, then a decline which typically follows such an incident may well involve not only the impressive "trophy fish", MO/Lefle 5axata1o, but also the other desired species such as largemouth bass that have maintained an almost legendary fishery in the southwest for many years (Minckley 1973).

The comments of Dr. Minckley are certainly valid, and I believe are shared by both State Agencies responsible for the management of the Lake Mead striped bass, but at present, investigations of the striped bass or

threadfin shad, which sustain the population, are only proposed.

Largemouth bass

The largemouth bass, WcAeptows safmoides, on occurred

throughout the Great Lakes region, south to the Mississippi River basin,

into northern Mexico and Florida, and north into the Carolinas and Vir-

ginia (Moore 1968). The origin of the generic name is from a deformed smallmouth bass that had the appearance of two separate dorsal fins;

W.cuptow means short fin. Satmo.ides means troutlike. As the largemouth bass gained the respect of anglers, it was indiscriminately stocked

in lakes, streams and ponds throughout the United States. Bass first

appeared in the Southwest in 1847 when they were introduced into Cali-

fornia (Emig 1966). The largemouth bass was probably well established

in both Arizona and Nevada by 1900. An extensive summary of the

introductions of largemouth bass is compiled by Robbins and MacCrimmon

(1974). 123

Distribution and abundance

This was one of the first species released into Lake Mead as the reservoir was filling. NPS records indicate that approximately 480,000 largemouth bass were released into Lake Mead between 1935 and 1940

(Table 24). Typical of a newly created impoundment, conditions were favorable for an "explosion" of the bass population and they quickly spread throughout the lake. Although largemouth bass have apparently declined in numbers since 1974, they are still abundant throughout the reservoir. Bass were not collected in the mainstream Colorado

River, but were occasionally observed in backwaters below Surprise

Canyon and at the mouth of Spencer Creek.

The vertical migration begins in late March or April. Individuals and small schools of yearlings begin to enter the shallow water followed by older adults. The first fish to arrive are mostly females and they begin to pair with males almost immediately. By August, bass fry are swarming in shallow water (1-2 m) and yearlings and adults are normally seen in water 2-5 m deep. Larger adults begin to move into deeper water and by the last week of October, they are rarely seen along the shore. Small, fragmented schools of young bass remain for one or two weeks longer in and around vegetative cover. Anglers report best results at a depth ranging from 8 to 15 m during this time of year. In late February or early March, adults move into shallow water near rock piles and inundated salt cedar.

Reproduction

In Lake Mead, largemouth bass begin to spawn when water temperature reaches 15-16°C in March or early April. Spawning continues into June. The nests are usually built by the male in water 1-3 m 124

Table 24. Summary of largemouth bass stocking records for Lake Mead, Arizona-Nevada 1935-1977.

Year Number released

1935-1939 480,625

1939-1942 286,090

1975 13,343

1976 11,306 1977 10,016 125

deep. Some nests have been found in water 8 m below the surface

( Allen and Romero 1975). The nests are typically about 13-15 cm deep, depending on the substrate, and from 0.5 to over 1 m in diameter.

Once the nest is constructed, the male herds the female to the nest site where the gametes are simultaneously released. The female is then driven away and the male remains as a guardian. Each nest may contain from 2,000 to 94,000 eggs which hatch in about two to five days. The emerging sac fry form into swarms that remain near the nest site for

8-14 days. The male is very defensive and protects the fry until the swarm begins to break up. Allen and Romero (1975) have demonstrated that the conditions for successful reproduction and survival of bass in Lake Mead are improved in the years that the water level is not drastically lowered. The impact of water level fluctuation on success of largemouth reproduction in Lake Mead is being closely examined in a joint investigation of NDW and AGED. Any comments at this time on the factors involved with nesting success or survival would be speculative and premature.

Age and Growth

The circuli were fragmented in approximately 80 percent of largemouth bass scales which made precise aging difficult. Normal annulus formation seems to take place in late January or early February. Average growth during the first year is 15.2 cm TL; other studies report similar first-year growth between 13.5 and 20.1 cm TL (Jonez and Sumner 1954,

AGFD 1965, Minckley 1972). The fastest growth of young-of-the-year fish was 26.2 cm during the early years of the reservoir in the 1940s

(Moffett 1943). Following the introduction of threadfin in 1954, growth of largemouth increased after class II, but young-of-the-year bass grew slower perhaps due to competition with the shad for zooplankton. Due to 126

the scarcity of benthic invertebrates, plankton are critical to the young

of all gamefish in Lake Mead. Zooplankton dominate the diet of young-of-

the-year bass until their second summer when they begin to consume larval

and juvenile shad. Growth is the greatest for yearling fish (16.6 cm).

Average annual growth for class II and III bass is about 5 cm, and then

declines to only 1 or 2 cm for age classes IV through VII (Table 25).

Largemouth bass may live up to 12 years (Emig 1966, Scott 1967)

except in the southern states where the maximum age may reach 16 years.

A life expectancy of 8 to 10 years for largemouth in Lake Mead is realis-

tic. Jonez and Sumner (1954) aged a largemouth bass weighing 4.5 kg at

eight years of age. The largest bass collected during this study was a 490

mm male in his seventh year of life, but there are reports of fish weighing

5 kg that may have been older. Creel information reveals that most of

the largemouth bass taken from Lake Mead are three years old or less

( NDW 1974-1977). Condition factors of the fish collected during this

survey ranged from 0.51 to 1.99, with an average of 1.28. These values

.are slightly higher than those obtained in 1971 when Minckley (1972)

reported condition factors of 1.016 for males and 1.018 for females.

Food habits

Young-of-the-year bass normally rely almost exclusively on plank-

tonic crustaceans and aquatic insect larvae and pupae. The shift from a

planktivore to a piscivore usually occurs between 32-104 mm TL, depending

on the availability and size of the forage species. In Lake Mead, this

shift begins at a length of 40-51 mm TL (Baker and Burk 1976). The

stomachs of fish less than 100 mm TL that I examined contained large

numbers of shad larvae and fry. They may also begin to prey on their

fellow bass fry several weeks after the swarms leave the nest. A num-

ber of bass in each swarm are noticeably larger as early as six to

eicht weeks after hatching, presumably r'ue to cannibalism. Similar 127

Table 25. Average growth (cm) at scale annuli of largemouth bass in Lake Mead, Arizona-Nevada.

Year 1 II III IV v VI VII

1943 26.2 32.0 34.0 37.1 38.6 41.7

1954 13.5 26.2 34.8 41.7 47.0 52.1

1965 18.5 24.2 35.6 40.1

1972 20.1 31.5 35.8

1978-79 15.2 31.8 36.2 41.8 46.0 48.1 49.0

Authorities:

Moffett, 1943 Jonez and Sumner, 1954 AGE, 1965 Minckley, 1972 128

observations are reported by Moyle (1976).

The wide gape of this species admirably suits the adult for foraging

on fish and crayfish. Before shad were introduced, crappie and bluegill

were the dominant forage fish for bass 51-205 mm TL (Moffett 1943, Jonez

and Sumner 1954). Shad are now the mainstay of the diet of adult bass; bluegill, crappie and channel catfish are secondary food items. Fry

and fingerlings of their own species are also common in the diet (Roden

1979). Cannibalism becomes more evident in waters similar to Lake Mead

that lack adequate vegetative cover and concealment for smaller fish.

Present status and significance to the fishery

Historically, Lake Mead was renowned as an excellent largemouth bass fishery. In the late 1950's and early 1960's, the number of bass harvested from the lake was consistently over 400,000 each year. Dur-

ing this period, well over 60 percent of fish in anglers' creels were largemouth bass. A downward trend in bass production began to appear in 1963 which was partially attributed to the reduced water flow into

Lake Mead while Lake Powell was filling. There was a steady decline in the number of bass taken from the reservoir from 1967 to 1971. In

1971, less than 190,000 bass were caught. The bass fishery recovered briefly in the early 1970's, but by 1977 largemouth bass were third to channel catfish and black crappie in anglers' creels. Only 136,000 bass were caught that year representing less than one-fourth (24.5) of the total catch (NFG 1958 through 1977). Avid largemouth bass fishermen were not easily discouraged, but as fewer bass were harvested each year and the striped bass gained popularity, the number of laraemouth bass fishermen dropped from 29.3 and 40.2 percent in 1975 and 1976 to 32.9 percent in 1977 (NFG 1975, 1976, 1977). 129

In the past, largemouth bass have been the focus of most of the

fisheries research activities conducted on Lake Mead (Moffett 1943,

Minckley 1972, Allan and Romero 1975, Jacobson 1977, 1978). When creel

census data indicated the numbers of bass were declining in the reser-

voir, the obvious causal factor was the impact of the fluctuating water

levels on this and the other fish species. Hopefully, the impact of

water drawdown on the nesting success and survival of the largemouth

bass population will be determined in the near future with the comple-

tion of a five-year joint investigation by AGED and NDW. Initial

results indicate declining water levels may have contributed to a 25

percent loss of bass nests (Jacobson 1977).

Lake Mead and other reservoirs behind hydroelectric dams are

unstable systems at the mercy of the demand for electrical power and

downstream irrigation. It is my opinion that in recent years the

largemouth bass has been the victim of the exigencies associated with

the drawdown of surface water, particularly during the spring spawning

season. The stability of a reservoir is one of the most crucial factors

that dictates which fish species will occur there and the size of the

populations. The largemouth bass is generally characteristic of

stable habitats and is poorly adapted to thrive for long periods in

fluctuating environments such as Lake Mead.

Since this study was not designed to address the impacts of the water level fluctuations on the fish communities, there are little

abosolute data herein to support these basic ecological principles.

However, there are data to show the rising and falling lake elevation

does prohibit the establishment of the benthic invertebrate community

which is an important trophic compartment providing the largemouth bass

with a suitable-sized food source during its transition from a planktivore - 80 total number harvested percent total catch 70

• 60 1 0 1.ua3.Aad

[50 Lel.o; JOglUrIU 400,000 [. 40

1 110Q.ED , 30 [email protected]

1 200,000

- I IL. 1 1 I--■ FL+ l•-■ -1-17 10 1-0 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 Ul 01 01 01 01 O C al 01 01 t../1 01 V ■ -.1 NJ NJ s,1 Co t-C) C.) 4 CTI CI V CO 10 0 -12=. 01 01 NI Figure 5. Estimates of total harvest and percent total catch of largemouth bass from Lake Mead, Arizona-Nevada, 1953-1977. 131 to a piscivore. Regular dessication of the littoral zone not only precludes the permanent growth of aquatic plants which harbor many aquatic invertebrates, but also is responsible for increased predation of young fish when they are unable to find adequate cover and concealment.

Several objectives of a management program for the Lake Mead fishery should include an increase in the average size of gamefish, and increase in the numbers of gamefish, and the addition of the missing invertebrate trophic level (s). All of these goals have been realized in studies monitoring fish communities in unstable systems once the system was stabilized (Orians 1969, Fleming 1973, Kushlan 1976).

Perhaps once the data from the current largemouth bass investigations are analyzed and interpreted, the first management recommendation will be simply to give more attention to the importance of reservoir fishery and the recreation it provides when manipulating water releases through Hoover Dam.

Bluegill

Bluegill, Lepomis machAocUAws, are common in lakes, ponds and streams in Arizona and Nevada, and the reservoirs of the Colorado River.

They are easily identified by a flexible black flap at the rear of the operculum, faint vertical bars along the sides and relatively long pointed pectoral fins ( manochOw means large hand in Latin, referring to the elongated pectoral fins). Bluegill are deep-bodied and laterally compressed fish with small terminal mouths. Color varies from dark- olive to black along the dorsum becoming light green or grey along the sides and ventrum. The sides have vertical dark bands with yellow or bronze between the dark bars. Breeding males are black or black-purple particularly on the nape and the breast is brilliant orange or bronze.

They can tolerate a variety of aquatic environments but are typically 132 found near rooted aquatic plants in shallow water (4z5m) of ponds and lakes.

The bluegill is a native of the warm waters of the United States from southern Quebec and Manitoba in Canada south through the Great

Lakes Region and Atlantic Coast of the Mississippi Drainage, west through the gulf states and northern Mexico, and north through the Pecos

Drainage in New Mexico (Eddy 1957, Schneberger 1972). As with other members of their family, they have spread rapidly. Occurring in every state except Alaska, they are probably the most widely distributed centrarchid (Walden 1964).

One of the first releases of bluegill in the Southwest was in Utah in 1980 when a "mixed group of sunfish" was stocked in the Weber River and Utah Lake (Sigler and Miller 1963). They were first reported in

California waters in 1908 (Curtis 1949) and were first stocked in Nevada in 1909 (La Rivers 1962). Probably in Arizona waters by 1900, bluegill are now ubiquitous. They are commonly used to stock farm ponds and small urban fisheries, but in these situations stunting frequently occurs and quality fishable populations are rare.

Distribution and abundance

Bluegill were introduced into Lake Mead when an unknown number of fish were stocked from 1937 to 1942 (Baldwin 1945). They established quickly and became the second most abundant gamefish in the reservoir in the early 1940's (Moffett 1943). Today, they are the most abundant centrarchid in the Lake.

During this investigation, a total of 221 bluegill was collected by seining, electrofishing and gill netting. Bluegill were collected in all of the major basins, but they were not collected or observed at any of the 13 fish collecting sites along the Colorado River from Separation

Rapids (rivermile 239.6) to Emory Falls Canyon (rivermile 274.4). They 133 do occur in the Colorado River in small numbers based on one record of a bluegill from Spencer Creek (Suttkus et al. 1970).

Sumner (1952a) noted that small bluegill remained in schools at depths of 3 to 6 m near submerged Tamalix in July. The larger adults

(76-127 mm) tended to frequent bushy areas closer to shore in water

1 to 4 m deep. Although they are scarce, bluegill are still present in shallow water in October. By November, most have moved into deeper water, but a few adults were observed near the shore throughout the winter. In late February and early March, they move up along the shores, staying close to inundated Tamnix and dormant aquatic vegetation during the daylight hours. At night, they are commonly seen near the shore in open areas near rock ledges.

Reproduction

Spawning usually begins when water temperature reaches 18-21 °C.

In Lake Mead spawning commences in April and may last through August.

Sumner (1952a).collected several adult males in late August that were still in nuptual colors and ripe. The male excavates the nest with his tail forming a depression 25-30 cm across and about 5-12 cm deep. Nests are usually built in shallow water 0.5-1.5 m deep but in Lake Mead nests have been found in water over 3 m deep (Jonez and Sumner 1954). The male attracts the female to the nest site by courtship displays and grunting sounds and the pair spawn side by side. From 2,000 to 50,000 eggs are deposited depending on the size of the female, and the clutch is closely guarded by the male.

The eggs hatch in about two to three days at 20°C and the fry begin to seek cover immediately.

Age and growth

Generally bluegill grow to 4-5 cm TL their first year with 134 subsequent annual growth increments of 3-5 cm. Growth rates are highly fluctuant varying with water conditions, but seem to be best in uncrowded systems that range from 15-25°C. They may live to an age of eight or nine years. A typical Lake Mead bluegill is about 12-16 cm and four or five years old. The fish collected during this survey were relatively small (14-195 mm) averaging 34.4 gms.

Food habits

Bluegill are highly opportunistic feeders that usually prefer larvae of aquatic insects or planktonic crustaceans. They may also consume snails, crayfish, adult insects and the eggs of other fishes.

When invertebrates are not available, plant material oftem comprises a major part of the diet. Food habits studies of Lake Mead bluegill show they utilize insects, followed by plant material and fish (Jonez and Sumner 1954). The diet changes with the season: large quantities of planktonic crustaceans consumed during the early spring and winter; during the summer, the diet consists of chironomids, water mites, dragonfly larvae, and ostracods (Deacon et al. 1972).

Significance to the fishery

Bluegill are often underestimated as a gamefish because of their relatively small size. Because they are easy to catch, they are favored by children, young adults, and warm-water fly fishermen.

Where they occur, they are usually numerous and can be taken with a variety of baits and artificial lures. In some Arizona lakes and ponds, they are enthusiastically caught at a rate of more than 100 fish per angler day.

Bluegill were most important to the Lake Mead Fishery in the 1940's 135

and 1950's as a forage fish for the largemouth bass (Moffett 1943, Jonez

and Sumner 1954). From 1958 to 1967 the estimated number of fish har-

vested range from about 5,000 to 34,000 fish per year which represented

less than five percent of the total catch. They were most numerous in

anglers' creels in 1968 when over 130,000 fish were harvested. (Figure 6)

In recent years, they have maintained a relatively stable population,

perhaps because predation pressure has shifted to the threadfin shad.

Although angler effort has remained consistently below one percent,

which is the lowest for any of the major gamefish, an estimated 75,601 bluegill were caught from the reservoir in 1977, which represented 13.6 percent of the total catch (NFG 1958 through 1977).

Green sunfish

The green sunfish, Chaepobnyttus mulatto, is a stocky, laterally compressed fish with a large mouth extending below the anterior edge of the eye. The black spot at the posterior edge of the stiff operculum is outlined with a tan or grey opercular flap. The dorsum is olive- green, becoming lighter on the sides and shading to yellow or orange on the belly. They are easily distinguished from other sunfish in the water by the white or tan margins on the dorsal, anal and caudal fins, and the dark blotches on the rear of the dorsal and anal fins. The cheeks are lined with irridescent emerald-green streaks or broken lines that radiate posteriorly. Breeding males become darker on the back and sides, and the breast and fin margins become brighter. The green sunfish is an adaptable species that prefers rocky conditions in Arizona waters. They are commonly found in brushy banks, cliffs, or near rubble piles (Minckley 1973). Green sunfish seem to do best when other centrarchids are not abundant and in waters where 136 there are fewer than three or four other species.

There are conflicting opinions on the generic classification of the green sunfish between LeponiL6, as recognized by the American Fisheries Society, or Chaenobnyttu6. I concur with the opinions of Hubbs (1972) and Minckley (1973), based on the work of Bransen and Moore (1962), that the green sunfish is more intimately related to the warmouth,

Chaenotvtyttuz guto6ws (Cuvier), and should be retained within the genus

ChaenobItyttus.

The native range includes the eastern United States from the

Great Lakes to Mexico, and the Alleghenies to the Mississippi River.

Green sunfish were accidentally release in California in 1891 (McKechnie and Tharratt 1966) and spread rapidly (Moyle and Nickols 1973). They are now common in California, absent only from the Klamath River system (Kimsey 1956, Moyle 1976). Green sunfish were planted in the

Weber River and Utah Lake in the state of Utah in 1890 (Sigler and

Miller 1963), and they are now widespread in the state (Wright 1951).

Little information is available regarding specific introductions of green sunfish into either Arizona or Nevada. The first documented occurrence of green sunfish in Arizona was in 1926 (Miller and Lowe

1967), but the sunfish probably had been introduced in both states by 1900. A primary vehicle of dispersion for the green sunfish has been, and is today, some well intentioned fishermen and biologists.

Distribution and abundance

Green sunfish were first introduced into Lake Mead from 1937 to 1939. There are apparently no records showing the number of fish or the exact date(s) of release. The California State Central Valley

Hatchery transferred 300 green sunfish to the state of Nevada in 1939: 150,000 20

125,000 total number harvested

percent total catch I t / t \- - 15 1 t / i I 100,000 I / ' I / I

/ I I / I i I 1 1 /- '-\

TE10j, / \ I . / 75,000 \ 1 1.-- --/ \ / - 10 \ /

S9A-IVII I

I V

50,000

/ \ / \ I 5 / \ I 25,000 / N/

1 I 1 i l 1 1 I 1 I 1 1 1 1. -. I--• - 1..N. 1.-+ l•-• 1■., I-+ I.-. I-, 1.-.. 1 4 1 4 1 4 1/40 VD vD /.0 /.0 1/40 /0 1/40 VD VD VD VD VD , , , , , t.0 ‘.0 V.") VD Li' CS CT ON CT a a a a a -../ .....I ....j ....1 ....J -.I -4 1/40 0 IV La .0- Ln ON s4 CO VD 0 1--• ts.) 1.....) .P. VI CA

o - Figure 6. Estimates of total harvest and percent total catch of bluegill from Lake Mead, Arizona- Nevada, 1958-1977. 138

the record does not show the disposition of these fish, but they might

have been placed in Lake Mead. Green sunfish could have easily been mixed with bluegills, or even stocked as bluegills, since they are

often misidentified. Nevertheless, green sunfish were documented in

Lake Mead by 1938 (Miller and Alcorn 1945).

During this survey, seventy specimens of green sunfish were

collected. They were collected or observed near the shore and in

open water in all of the major basins. Most green sunfish were collected by electrofishing (5.76 fish/hr) and netting (0.02 fish/hr).

Only seven specimens were from seine collections. Size ranged from 49 to 180 mm TL; the mean length was 97 mm TL.

Reproduction

Reproduction of the green sunfish is similar to that of the bluegill, with a few exceptions. In Lake Mead spawning occurs from

March into July; several active nests with eggs were observed in

late July. Spawning activity may continue into early August during years of cooler water temperature. Nests are usually concealed by large rocks on rock shelves and ledges.

Typically, nests are built in colonies in shallow water (Carson

1968). In Lake Mead nests are found from 0.5 to 3.0 m deep. Nests are relatively small, constructed about 35 cm in diameter and spaced

3-4 m apart. In other Arizona waters nests may be more closely spaced within 30-50 cm of each other (Minckley 1973). Eggs hatch in about 50 hours (@23.8°C) and larvae are free-swimming in two days (Childers 1967). Post larval growth is described in detail by Meyer (1970). The fecundity of green sunfish collected in July 139

ranged from 18,000 - 21, 000 (i = 20,600).

Age and growth

The age and growth patterns of green sunfish were determined by

scale annuli analysis. The validity of this technique as applied

to green sunfish has been verified by Hubbs and Cooper (1935) and

Sprugel (1955). Green sunfish are fully scaled at a length of 17 mm

and at 22 mm ctenii are present (Hoffman 1955). In general, green sunfish show the best growth in lake environments (Jenkins et al.

1955), especially in clear waters (Hubbs and Cooper 1935). Male sunfish normally grow faster than females (Hansen et al. 1960,

Childers and Bennett 1961) and are usually longer lived (Huffman

1955). Longevity ranges from four to seven years (Flower 1952).

They may rarely live to ten years (Purkett 1958).

Growth measurements of Lake Mead green sunfish in the early

1950's revealed yearling fish grew about 49 mm FL. The largest fish from that collection was 152 mm TL in its sixth year of life

(Jonez and Sumner 1954). Growth rates of adult green sunfish determined from this study are comparable to earlier data, but data from the 1978-1979 collections indicate a decline in the rate of growth during the first year of life. Converting fork to total lengths with the factor 1.46 (Hansen et al. 1930, Carlander

1949), yearling fish averaged 59 mm (8 mm less than the annual growth measured in 1954). The slower growth the first year may reflect increased competition for the available food with other centrarchids and particularly threadfin shad. Similar to largemouth bass and black crappie, the green sunfish shows the 140

greatest growth the second year as they become more piscivorous and are able to forage on their earlier competitor, the threadfin shad.

Condition factor (K) ranged from 1.4 to 1.8, with a mean of

1.5. There is a marked increase in K as the fish increase in length.

This is not uncommon for the species (Hauser 1963, Muench 1963).

The condition factor for Lake Mead green sunfish is slightly lower but still comparable to other reservoir populations (Ruhr 1952,

Nelson 1962).

Food habits

The diet of the green sunfish typically includes aquatic invertebrates and fish. This species has the flexibility to shift to a diet of algae and plants if the preferred foods are not available. In the early 1950's, 20 percent of the diet of green sunfish was fish. Black crappie, bluegill, largemouth bass and other green sunfish were identified in stomach samples (Jonez and Sumner 1954). A more recent study indicated a seasonal shift from gastropods during the winter to water mites and midges in the spring and summer (Deacon et al. 1977).

Present status and significance to the fishery

Large green sunfish are rare in Arizona. They are one of the most prolific centrarchids and stunted populations soon develop that offer little value as sport or food. Their abundance has been negatively correlated with the abundance of other species (Mogle and Nickols 1973). It is unfortunate that this sunfish has become established in reservoirs of the Colorado River since they usually do not interest adult anglers. This is a prime example of the senseless introduction and of subsequent dispersion of an 141

undesirable fish species by anglers and careless fisheries managers.

Black crappie

The black crappie, Pomoxi nigitomacutatu, is a deep-bodied, laterally compressed centrarchid with a relatively small head and protruding lower jaw. The sides and back and dorsal, anal and caudal fins are spotted with dark grey or black blotches (Nigito- macutatm means black-spotted). The nape and pre-dorsal are darker than the rest of the body and the belly is typically white or dirty-white. Breeding colors are almost jet black, especially the anterior half of the body. Both the black and the white crappie, P. annutaAAo, occur in Arizona and Nevada. Crappie are frequently found near rooted aquatic vegetation in ponds and lakes that are warm and clear (Moyle and Nichols 1973). They are less abundant in streams, cold reservoirs and turbid river backwaters.

To the best of my knowledge, the white crappie is not found above

Hoover Dam. This confirms the results of Hansen (1951) and

Goodson (1966b) showing the black crappie generally prefers clearer, cooler habitats.

The black crappie naturally occurs from the Gulf Coast of

Texas east to Florida, north on the Atlantic coastal plain to

North Carolina and west in the Mississippi River system. Their native range also extends into Canada from Manitoba through the

Great Lakes to Quebec. Information on the first appearance of crappie in the southwestern U. S. is sketchy. They probably were introduced along with other centrarchids when largemouth bass were stocked during the late 1800's (Curtis 1949, Sigler and Miller 1963). 142

Distribution and abundance

Black crappie were stocked into Lake Mead soon after it began filling (Baldwin 1945, Wallis 1951), apparently released with bluegill.

In the early 1950's "tremendous numbers" of crappie were observed in water 3 to 4 m deep. Most of the observations were large schools

(100-500 fish) of relatively small fish (>100 mm) (Jonez and Sumner

1954).

Crappie remain in the shallow waters of Lake Mead until spring when they begin to disperse into deeper waters as surface water warms. Largemouth bass may actually prevent crappie from leaving a shallow area where they are easier prey. Bass "herding" may con- centrate crappie for short periods, but probably not for several months as suggested (Sumner 1952b). By October crappie are at depths from 12 to 60 m and are rarely seen along the littoral zone.

Only seven specimens of black crappie were collected during this investigation. All were taken with electrofishing gear from

Gregg Basin. These data extremely underestimate the number of black crappie in Lake Mead. NDW estimated that over 150,000 fish were caught by anglers in 1977. The few fish in these collections is attributed to the fact that this is a gregarious schooling species that randomly wanders throughout the reservoir, spending most of the time in the deep water regions. Crappie were commonly collected from open water by NDW while trawling for shad (Roden 1979). The deep-water habits were strikingly illustrated in June of 1962 when the U.S. Geological Survey exploded nine underwater test explosions at a depth of over 60 m in Las Vegas Bay. Approximately one million 143

juvenile crappie (2.5-5.1 cm) were killed.

Reproduction

Crappie slowly develop gonadal tissue through the fall and winter

( Morgan 1951) reaching peak reproductive condition as water temperature approaches 12.80C. Initial spawning behavior has been observed in

California and Utah to occur when temperatures reach 14.4-17.8°C

(Curtis 1949, Sigler and Miller 1963). In Lake Mead spawning occurs in March which closely coincides with spawning activities of largemouth bass. Spawning male crappie are the first to enter shallow areas to establish territories. The younger males casually move into the area first where there is usually territorial fighting for the best nesting sites (Ginnelly

1971). In Lake Mead, crappie nests are located 1-14 m deep on rocky slopes that vary from gentle to steep. Nests are similar in construction to largemouth bass nests but they are usually found near several large rocks or boulders.

Spawning behavior was not observed during this study. The following describes the courtship and spawning behavior of black crappie observed in

Roosevelt Lake, Arizona:

. . . Upon the arrival of the females, males began to move in frenzied circles which seemed to follow the rough outlines of their territory. Once the female had been attracted to an individual male he began to make rapid sideways sweeping movements using the caudal fin on the bottom substrate. After 20 to 30 of these sweeping movements a depression of six to eight inches in diameter was formed in the bottom gravel. Males then began a series of swimming motions around the female. At this time he began to bump her sides and belly. The bumping action brought about a series of discharges of eggs - she swam slowly away. The male then made a number of slow passes over the site apparently releasing sperm. This spawning procedure lasted approximately 20 minutes from the initial bumping to final fertilization (Ercole 1968). 144

Age and growth

• Growth of black crappie is generally good in Lake Mead and compar- °Vier able to growth patterns in large reservoirs that thermally stratify. NDW has recorded several crappie weighing over three pounds (Roden 1979).

When black crappie reach a length of about 50 mm, they are able to utilize threadfin shad as a food item and growth accelerates until the fish attains an age of about six years. Few fish reach seven years of age (NFG 1976).

Prior to the introduction of shad into the lake, black crappie were apparently able to subsist quite well on zooplankton, small bass and sunfish.

The population was considered "good with a few isolated cases of poor condition" in the 1950's (Jonez and Sumner 1954). The overall effect of the threadfin shad on the growth patterns of crappie in Lake Mead is difficult to assess but one other study has shown the value of K increased markedly soon after shad were established as a forage base (Beers and

McConnell 1966).

The condition factor for black crappie collected in 1978-1979 ranged from 0.85 to 1.59 with an average of 1.21. Although fluctuations in growth rate of crappie may be sex-related (Vanderpuye and Carlander 1971), there were no marked differences in value of K for male and female fish taken during this survey. The sample size was not large enough to examine condition factor in relation to fish of different year classes but other studies show one of two trends; either the value increases steadily until fish reach an age of four years (Elliot 1948) or K remains stable with only slight fluctuations with increased length (Sprague 1959, Beers and McConnell

1966). Condition factor data for black crappie in Roosevelt Lake, Arizona, indicate K is the lowest in June and July and highest from October to 145

February. Since the cooler water temperature of Lake Mead delays the production of gonadal tissue at least 30-45 days compared to the Roosevelt

Lake population, values of K would be expected to peak in late February and

March.

Food habits

Crappie are primarily mid-water feeders. Younger fish prey on aquatic insects and zooplankton and the piscivorous adults feed predom- inately on fish and adult aquatic insects. In the 1950's, 30 percent of the diet of Lake Mead crappie was largemouth bass, crappie and bluegill

(Jonez and Sumner 1954). A more recent investigation revealed a shift to mostly invertebrate food items. Daphnia sp. dominate in the diet with other foods including chironomids, odonatids, snails and fishes (Deacon et al. 1977).

Present status and significance to fishery

Historically they have been a valuable gamefish in Lake Mead rival- ing the channel catfish for the second most abundant species in anglers' creels. Crappie comprised six to seven percent of all game fish taken from the lake during a two year period from 1952-1954 (Jonez and Sumner

1954) and was ranked the third most important game fish. The total number harvested has fallen below 50,000 fish per year only once in 1973.

Their greatest contribution to the fishery was from 1974-1977 when they averaged over 125,000 fish per year. Black crappie have averaged between eight and 18 percent of the total catch between 1958 and 1975. In 1976 and 1977, crappie represented 23.1 and 26.7 of the total harvest, respectively (Figure 7). In 1977 an estimated 148,000 crappie were caught which was second only to channel catfish (166,000). Although relatively large numbers of crappie are caught each year (NDW estimates 150,000 in 200,000 total number harvested

percent total catch 150,000 ,

125,000

RT SZU 41.1e0sAad 100,000

CR LP404 IN) — 15 < 75,000 c+ 140;PO

— 10 50,000 -

5 25,000 -

I ------— ------1 I I R R R, 7 , R, -7 - R-- R , T....., . t..--. 1--. 1--. 1-4 ----. I-. I--- i-- t--- i--. 1---. ...-.. i--- ij ---.. 1----■ i--. 1--. CO 'SD KR) KO KO KO KR) KR) KR) ( c) KO KO KO KO K.O KO KR) KO KIO CRI 0-1 CRL CY, cr. CR, cm 01 CI 01 CI *--.1 ---1 ■J ..4 .....1 ...4 ...... 1 -...4 CO C) I---, N.) C..) -A 01 01 --.1 00 CO CD__ 1---. 1%) (....) -1=. Ul 01 -...1 Figure 7. Estimates of total harvest and percent total catch of black crappie from Lake Mead, Arizona-Nevada, 1958-1977. 147

1977), they account for approximately one percent of the total angling

effort (NDW 1975, 1976, 1977). The incongruity of angler effort and total

harvest data may reflect the fact that crappie are caught and kept by

anglers seeking largemouth bass (33% angler effort in 1977).

NDW suggests that Lake Mead water fluctuations did not appear to have

stranded any black crappie nests in the early 1950's and probably did not

have any direct harmful effects on the spawning potential of the black

crappie (Jonez and Sumner 1954). Conflicting results on the impact of

fluctuating water levels are reported in a study of crappie in Roosevelt

Lake, Arizona. This investigation stated fluctuating water levels was

one of the more important factors influencing population levels of crappie

(Ercole 1968). This study suggested that seasonal fluctuation in the water

level may curtail successful spawns by exposing nests constructed in

shallow water. The exact effect of the water fluctuations on fish popu-

lations in Lake Mead, particularly largemouth bass, is being jointly

examined by the states of Arizona and Nevada with funding from WAPRS. The results should be available by 1983.

Predator pressure must be considered as a limiting factor in crappie

production. Angler reports of striped bass gorged with crappie are not

uncommon although the striped bass stomachs I have examined contained

mostly shad. Carp are also notorious predators of the eggs and larvae of

crappie (Ercole 1968, Ginnelly 1971). Carp have been observed consuming

eggs from unprotected centrarchid nests in Lake Mead and I have found

fish eggs in carp stomachs, but the eggs could not be identified to species.

Green sunfish x bluegill (hybrid)

A single green sunfish x bluegill hybrid was collected. Both the

bluegill and the green sunfish readily interbreed with other centrarchids 148

(Table 26) but natural hybridization in Arizona occurs in about 1 of 10,000 fish (McCall, unpub. data 1976). The specimen is morphologically similar to the bluegill with a deep, laterally-compressed body, moderately long pectoral fins, and a large opercular spot. The mouth is larger than that of a bluegill but does not reach beyond the anterior edge of the eye.

Coloration is similar to a green sunfish with white margins along the pectoral and anal fins and irregular irridescent lines on each side of the mouth.

Hypothetical Occurrences

Native species

Little Colorado River spinedace

The Little Colorado River spinedace, Lepidomeda vi.ttata, is limited in range to the north flowing tributaries and upper mainstream of the

Little Colorado River (Miller and Hubbs 1960, Blinn et al. 1977). Appar- ently the only record of the dace from the Lake Mead Recreation Area was reported from bait tanks at Las Vegas Wash and Boulder Beach near Lake

Mead in 1950 (Wallis 1951). The decline of the population is attributed to water manipulation, chemical poisoning, and interactions with introduced minnows. This species is listed under Group IV of the Threatened and Unique Wildlife of Arizona which states it is of special interest because of limited distribution in Arizona. The biology of the Little

Colorado River spinedace is discussed in detail byMinckleyand Carufel

(1967).

Virgin River spinedace

The Virgin River spinedace, Lepidomeda mottbspin,bs matioim6, is a rare native cyprinid that is now limited to the Virgin River and its tributaries in Arizona, Utah and Nevada. The native range has been 149

Table 26. Known hybrids of green sunfish, ChaenolAyttto cyanettws, and bluegill, Lepomis mactockau.s.

Parents Female Male Authority green sunfish X pumpkinseed Hubbs and Hubbs, 1931 C. cyanatus L. gibbo61.0 Hubbs and Hubbs, 1932 Etnier, 1942 green sunfish X redbreast sunfish Sitherman and Hester, 1962 L. autitta green sunfish X warmouth Lewis and Heidinger, 1973 C. guto6u4 Minckley, 1973 green sunfish X longear Hubbs and Hubbs, 1932 L. megatoti,s green sunfish X redear Lewis and Heidingel, 1971 L. micnotoplubs Childers and Bennett, 1967 green sunfish X bluegill Childers and Bennett, 1961 L. mautochilm Childers, 1967 green sunfish X (bluegill X redbreast) Smitherman and Hester, 1962 pumpkinseed X green sunfish Hubbs and Hubbs, 1931 Hubbs and Hubbs, 1933 warmouth X green sunfish Childers, 1967 Hubbs and Hubbs, 1933 orange spotted X green sunfish Hubbs and Hubbs, 1933 L. ham-Wis longear X green sunfish Hubbs and Hubbs, 1933 redear X green sunfish Childers, 1967 Childers, 1961 Minckley, 1973 bluegill X green sunfish Bailey and langler, 1938 Carbine and Applegate, 1948 Minckley, 1973 bluegill X rock bass Tyus, 1973 Ambeoptita nupeistiu: Hester, 1970 bluegill X flier Hester, 1970 CentAakchtbs mackopteitto 150

Table 26_ (continued)

Parents Female Male Authority

bluegill X blue spotted sunfish Hester, 1970 Epneacanthuz g1okio6a4

bluegill X redbreast sunfish Hester, 1970 Smitherman and Hester, 1962

bluegill X pumpkinseed Lagler and Steinmetz, 1957 Noland, 1951

bluegill X warmouth Merriner, 1971 West and Hester, 1966

bluegill X redear Krumholz, 1950

bluegill X largemouth bass Merriner, 1971 WcAopteAto )satmoidez West and Hester, 1966

bluegill X black crappie Merriner, 1971 Pomoxs micikomacutatu6 West and Hester, 1966

bluegill X (bluegill X redbreast) Smitherman and Hester, 1962

rock bass X bluegill Tyus, 1973

redbreast sunfish X bluegill Smitherman and Hester, 1962

pumpkinseed X bluegill Hubbs and Hubbs, 1932 Lagler and Steinmetz, 1957

warmouth X bluegill Hester, 1970 West, 1970

redear X bluegill Krumholtz, 1950 Ricker, 1948

largemouth bass X bluegill Hester, 1970 West and Hester, 1966

black crappie X bluegill Hester, 1970 Merriner, 1971 redear X (bluegill X redear) Smitherman and Hester, 1962 151 restricted by water manipulation, predation and competition with exotic species. Most of what is known of the life history of the spinedace is based on the work- of Rinne (1971). The Virgin River spinedace is included

in Group IV of the Threatened and Unique Wildlife of Arizona and is listed as rare on the Nevada Protected-Unique Species List.

There are three records of this species from Lake Mead; all from bait

shops near the reservoir. On August 31, 1938, C. L. Hubbs identified

Virgin River spinedace from a bait tank in Las Vegas, Nevada. The owner,

Mr. Clarence Alexander, had seined the fish from the Virgin River west of

Bunkerville, Nevada. 0. L. Wallis collected two specimens from a bait dealer at the Lake Mead boat dock on December 31, 1948, and three spinedace were identified from a bait box on Lake Mead in February, 1951, by

Al Jonez, NDW. These fish were reported to have come from the Santa Clara

River near St. George, Utah.

Moapa dace

The Moapa dace, Moapa cotiacea, is native to the Warm Springs region in northern Clark County, Nevada. They inhabit warm water seeps and springs

(87-93°F) that drain into the Moapa River and are rare in the lower portion of the river that has been inundated by Lake Mead (Minckley 1965). The

Moapa dace is listed as rare on the Nevada Protected-Unique Species List.

Woundfin

The woundfin, nagoptetm aAgemtbssimm, was historically common along the lower Colorado and Gila Rivers in Arizona and the lower Virgin

River in Arizona, Nevada and Utah. Today, they are found in the Virgin

River between La Verkin Springs, Utah, and Lake Mead (Bradley and Deacon

1967, Williams 1977). The only record of the woundfin from the Lake Mead

Recreation Area is a single specimen obtained from a bait dealer on June 152

(Miller 1952). 16, 1950/ Woundfin are included in Group II of the Threatened and Unique

Wildlife of Arizona which states the species is in danger of being eliminated from Arizona. They are also classified as rare on the Nevada Pro- tected-Unique Species List and are listed as endangered by the USFWS in

1970 (USFWS 1970). The USFS has drafted and is implementing a woundfin recovery plan, and a population is being maintained at Dexter National Fish

Hatchery, New Mexico.

In 1970, about 200 fish were released within the historic range at the confluence of the Paria and the Colorado Rivers but this attempt to establish another population in the Paria drainage was apparently un- successful. I have sampled this area several times in the recent few years but have not collected woundfin.

Humpback chub

The humpback chub, Gila cypha, was once common in the Colorado River from the present site of Hoover Dam (Miller 1955) to Flaming Gorge on the

Green River in Utah. They quickly disappeared from the Colorado River below Hoover Dam in the late 1930's as water releases through the dam lowered water temperatures. Chubs were able to persist above Lake Mead for a short while but began to decline in numbers in the Grand Canyon soon after the closure of Glen Canyon Dam in 1964. Their last refugium in

Arizona is the warm water confluence of the Little Colorado and Colorado

Rivers. Two other populations of unknown size occur at Desolation Canyon on the Green River in Utah and in Black Rocks on the Colorado River on the Utah-Colorado border.

The humpback chub is federally listed as an endangered fish (USFWS

1967) and appears under Group II of the Threatened and Unique Wildlife List of Arizona. A recovery plan is being implemented which includes the cap- 153 ture and rearing of brood stock for propogation purposes. In late January

1978, I assisted C. O. Minckley and personnel from the Museum of Northern

Arizona in collecting and transporting the first specimens of G. cypha to a hatchery for propogation. Eleven chubs were collected at the mouth of the little Colorado River, placed in plastic bags aerated with pure oxygen, sealed in styrofoam containers and flown by helicopter to the north rim of the Grand Canyon. The fish were then transported by car to Willow Beach

Fish Hatchery below Hoover Dam. Two other recovery trips were made in May,

1978, and October, 1979, which added an additional 26 adult fish to the brood stock (C. O. Minckley, pers. comm.). As of April 24, 1980, there were twelve remaining adult chubs from the Little Colorado population ranging in size from 10-19 inches TL (Roger Hamman, USFWS, pers. comm.).

Bonytail chub

A native of the Colorado River, the bonytail chub, Gita dcgans, could still be observed in large numbers in Lake Mead after the closing of Hoover

Dam (Moffett 1953). By 1950 they were rarely seen and few were taken by anglers (Wallis 1951). Once reported as "abundant" in the Colorado River shortly after the closing of Glen Canyon Dam, the bonytail chub is now believed to be extirpated from Glen Canyon Dam to Hoover Dam. Until the taxonomy of the Gila complex is better defined, it is presumed that the only "pure" population of this species inhabits Lake Mohave, Arizona.

The bonytail chub is listed in Group II of Threatened and Unique

Wildlife in Arizona and was recently given full protection in the state's fishing regulations. Nevada lists this species as rare, California classifies them as endangered, and they were listed as endangered by the USFWS in

April 1980 (USFWS Federal Register 4/23/80). The following statement was made by Orthello Wallis in 1951: 154

. . . It is evident that the native fishes of this (referring to Lake Mead) and other portions of the Colorado River basin are destined to become scarce or locally exterminated. It is regrettable that little can be done to save them, for our present knowledge of these species is very incomplete. Con- sequently, this fauna should become the object of more intensive research before it has disappeared completely or its composition has been altered further (Wallis 1951).

This statement was made almost 30 years ago and still applies today.

In late April, 1979, I assisted a USFWS personnel and a contingency from ASU (headed by W. L. Minckley) in collecting two G. eteganz (about

60 mm TL) from Lake Mohave and transporting them to Willow Beach Hatchery for propogation, but unfortunately both fish were females. The same area was re-collected in March and May, 1980, which added three more chubs to the brook stock. These fish were also females (W. L. Minckley, pers. comm.).

Colorado River (roundtail) chub

Roundtails in the 1940's were considered "common" (Moffett 1943) and "widely scattered throughout the lake" in the 1950's (Jonez and Sumner

1954). It is difficult to know which species was actually observed due to similarities in the Gita complex. It is possible that these fish were one of the several currently recognized subspecies of the robusta series, perhaps G. etegouvs or G. cypha, or hybrids of these forms (natural hybridization may be common among robusta, elegans and cypha). Nevertheless, roundtail chubs are recorded from Lake Mead and the Colorado and Virgin Rivers prior to the closing of Glen Canyon Dam (Smith and McDonald 1959). The

Virgin River chub, which some believe to be an integrade between robusta and elegans (Ellis 1914, Miller 1946, LaRivers and Trelease 1952), is now restricted to the Virgin River from Virgin, Utah, to Riverside, Nevada.

They are proposed for federal listing as endangered (USFWS 1978) and listed 155 as endangered on Nevada's Protected-Unique Species List. Arizona places the roundtail chub under Group IV of the Threatened and Unique Wildlife

List.

Colorado River squawfish

The Colorado squawfish, Ptychocheauz facia/3, also called "Colorado salmon" or "white salmon", was historically quite common along the lower

Colorado River. They now are restricted to the San Juan River in Utah and

New Mexico and the Green, Yampa and Gunnison Rivers of Utah and Colorado.

This is the largest of the American minnows (over 36 kg) (Jordan and Ever- mann 1896) that once provided an important staple for Indians along the river (Miller 1955). Squawfish were so numerous in the early 1900's that they were often removed from irrigation ditches with pitchforks and used for fertilizer.

Populations began to decline in Arizona during the period from 1930 to 1935 which coincides with the transformation of the Colorado River to

Lake Mead. Squawfish were still reported from Lake Mead in the 1940's but were rarely taken from the Colorado River after 1949 (Wallis 1951).

They are now extirpated from the Colorado River and its reservoirs in

Arizona. The last squawfish to be taken from the lake was in 1967 (Hinckley

1973).

This federally endangered species (USFWS 1967) has been the focus of concerned biologists in the upper Colorado basin for many years (Vanicek and Kramer 1969, Vanicek et al. 1970, Holden 1973). The reduction in range size, numbers and distribution of the Colorado squawfish is due to man's influence upon the aquatic environment. Seethaler (1978) lists the following as possible causes of the decline: stream pollution, parasites, competition, predation, change in prey, and fishing pressure. 156

A recovery team has been appointed and a recovery plan is completed and approved. Populations are being maintained in Willow Beach National

Fish Hatchery in Arizona, and Dexter and Hotchkiss Hatcheries in New

Mexico. In late March, 1980, 1500 fish (13-16") were tagged and transported from the Willow Beach to Moab, Utah, for release, and another

86 fish were taken to Logan State Hatchery, Logan, Utah.

Like the bonytail chub, the humpback chub and woundfin, the squawfish is listed under Group II of Threatened and Unique Wildlife of Arizona and classified as endangered by both California and Nevada.

Gila mountain-sucker

Considerable confusion exists over the taxonomy of the mountain- sucker group. In 1966, Smith combined the Gila sucker, Panto6teas and the White River sucker, Panto'stcas inteAmedi.us, as Catoistonws cCanki

(Smith 1966, Bailey 1970). I follow the nomenclature of Minckley (1973) who does not agree with this synonymy and has retained the genus Panto4teu4 for the mountain-suckers (See pages 63 and 64).

On December 31, 1948, O. L. Wallis collected two specimens of Gila mountain-suckers, Panto'stews etaitki, (reported as Utah mountain-sucker,

P. detph-(Inus utahenziis) from the Lake Mead boat dock. These fish were presumably seined from the Santa Clara River. The same species was still being sold as a bait fish on Lake Mead in 1951 (Miller 1952) and in 1954 (Jonez and Sumner 1954). LaRivers (1962) reported the suckers

(White River mountain-sucker, P. intekmediu/s Tanner) as an extensively used bait fish in both Lakes Mead and Mohave. NDW recognizes the Gila mountain-sucker (listed as desert-sucker) as a legal bait fish in waters common to Arizona and Nevada but Arizona does not authorize its use as bait. 157

Flannelmouth sucker x razorback sucker (hybrid)

Natural hybridization between the genera, Catostomus and Xytauchen, is well documented (Hubbs and Miller 1953, Holden and Stalnaker 1975).

Hybrids of the flannelmouth sucker, C. tatippin4s, and the razorback sucker, X. texanus, were collected in small numbers from tributaries of the Colorado River in the Grand Canyon in the early 1970's (Suttkus et al.

1976); pure specimens of the razorback were not taken.

Presumably, razorback suckers were more abundant than flannelmouth suckers in the Colorado River prior to the filling of Lake Powell in 1964 and hybridization was common. Following the construction of Glen Canyon

Dam, water temperatures declined and so did the number of razorback suckers.

The flannelmouth was more tolerant of the cold water and was able to successfully reproduce in the warm water tributaries. The few hybrids of the two species were eliminated genetically by the more abundant flannelmouth sucker.

A recent survey of the fishes of the Colorado River within the Grand

Canyon revealed good populations of flannelmouth suckers and bluehead mountain-suckers, but the razorback, or razorback x flannelmouth hybrid, has not been collected from the river or its tributaries (Carothers and

Minckley 1980). A single razorback was taken in 1978 from a trammel net set at the mouth of the Paria River and another razorback, or razorback hybrid, was observed but unfortunately escaped before it could be positively identified (C.O. Minckley, MNA, pers. Comm.).

The only area where these two species could co-exist and perhaps hybridize in the Lake Mead Recreation Area is the mainstream Colorado

River above Bat Cave (rivermile 266.5) to Separation Rapids (rivermile

239.6). However, it is doubtful that these species co-exist since flannel- 158 mouths are extremely rare in this section of the river and razorbacks have not been collected from Bright Angel Creek to Lake Mead (to the best of my knowledge).

Introduced Species

Freshwater eel

Freshwater eels, ANGUITTA NOZTTATA, were stocked in Utah during the late 1800's but disappeared soon afterwards and have not been reported since the turn of the century (Sigler and Miller 1963). In Colorado hatcheries, they have been raised from elvers to adults up to three feet in length (Everhart and Seamon 1971). Two specimens are recorded from

Lake Mead; both were caught by anglers in Overton Arm and Las Vegas Bay in 1972. One of these fish was given to a bait shop and later recovered by NDW personnel. The incidental occurrence of two specimens of eels from Lake Mead is surprising. Their origin into Lake Mead, as suggested by W. L. Minckley (1973), may be attributed to the accidental release from ballast tanks of marine watercraft or perhaps "bait bucket" introduction.

"Walking" catfish

Brought to the U.S. by aquarium traders, the "walking" catfish,

CtaAia4 bat/Lachuz, is native to Africa and southeast Asia. The catfish is an aggressive competitor that has little value, except to aquarium enthusiasts. Its tenacious characteristics and capabilities to disrupt or destroy established fisheries have warranted its prohibition by both

Arizona and Nevada (Col. River Wildlife Council 1977). In June of 1971 the NOW recovered two albino walking catfish from Lake Mead. Both were taken from Rogers Spring near the Overton Arm of Lake Mead; probably released by tropical fish collectors. 159

Green swordtail and southern platyfish The green swordtail, Xiphophoitto hateti, is a common aquarium fish that occasionally becomes established in warm springs and canals where they are released by aquarists. In Arizona, it has been taken from Rock

Springs, Maricopa County, and the Aqua Fria drainage prior to the 1965 flood (Minckley 1973). The swordtail and the southern platyfish, X. macutata, were established in Rogers Spring near the Overton Arm in the early 1960's (LaRivers 1962) but both species were unable to maintain reproducing populations (Deacon et al. 1964).

Smallmouth bass

Smallmouth bass, Mictoptekto dotomieui, were first released in

Nevada in the Carson River and Washoe Lake in 1888 (LaRivers 1962) and were established in Arizona prior to 1940 (Miller and Lowe 1967). This bass occurs along the mainstream of the lower Colorado River but it has not been collected above Hoover Dam. A single smallmouth bass was observed in 1942 near the mouth of the Moapa River by Dr. C. L. Hubbs (Miller and

Alcorn 1946). To the best of my knowledge, this is the only record of this species in the reservoir.

Walleye

Walleye, Stimstedion vitteum v.ituum, were released in Arizona waters in the mid-1960's (Minckley 1973). They were taken in the Colorado

River below Glen Canyon Dam in 1967, 1971 and 1972 (Stone 1967, 1971,

1972) but soon disappeared. At least two walleye have been documented from Lake Mead (Cal Allan, NDW, pers. comm.) although they have not been officially introduced into the lake. It is likely the two specimens passed through Glen Canyon Dam from Lake Powell, where they are common.

Field and Stream Magazine reports the walleye population in Lake Mead 160

"is expanding." Unless the authors have privy information, their state-

ment is erroneous and unjustified.

Convict and banded cichlids

The convict cichlid, Cichtcbsoma nigto6a2sciatum, is sporadically

established in the warm waters of central and southern Arizona (Minckley

1973). Large populations of this species were established in warm springs

flowing into Lake Mead from Nevada in the 1950's and 1960's (Deacon et al.

1964, Hubbs and Deacon 1964). Cichlids are prolific pugnacious fish that

compete with and destroy populations of native fish and warm water game

species. Although they present no threat to the Lake Mead fishery at the

present temperature regime, further spread of either the convict or the

banded cichlid should be watched closely and curtailed where possible.

Goldfish

Goldfish, Caltazsito autatm, are probably present in all major reservoirs of the lower Colorado basin but they do not achieve great abun-

dance. The first records of goldfish introductions in Arizona and Nevada

are sketchy. A report by Mrs. James Sharp of Blue Eagle Ranch, Nevada,

places the first plants in Nye county, Nevada, prior to 1900. Their occurrence in Lake Mead bait shops was first noted in 1951, and they are reported

from the reservoir in 1958 (LaRivers 1962). In 1975, four goldfish were collected from Lake Mead in Las Vegas Wash which were assumed to have been released in the upper end of the wash (Roden 1978). Both Arizona and

Nevada allow the use of goldfish as a bait fish in Lake Mead. Other than

its popularity as a bait fish, its contribution to the Lake Mead fishery is

insignificant at present and probably will remain so.

Golden shiner

The golden shiner, Notcmigonto ch.zy.!+acucu,s, is a native of the 161 eastern U.S. that is regarded as one of the most valuable species to the baitfish industry. They first appeared in Arizona bait shops prior to the 1930's (Miller and Lowe 1967). The shiner is a legal bait fish in

Arizona, Nevada, and California where the Colorado River is a mutual boundary and it is commonly used in Lakes Mead and Mohave. Unfortunately, once the golden shiner is established it has proven to be a serious competitor with trout in Arizona and has contributed to the decline of many of the native southwestern fishes (Minckley and Carufel 1967, Minckley and

Deacon 1968).

Reds_ide shinen

The redside shiner, Richatdzomius batteatms hydupheox, is a native on the Bonneville Basin and the Snake and Columbia Rivers (Sigler and

Miller 1963). They were found to be common in bait houses along the Colo- rado River in 1950 (Miller 1952) and were frequently used as a bait fish in Lakes Mead and Mohave in the early 1950's (Jonez and Sumner 1954).

Because they feed on the eggs and young of fish, they were first thought to be a potential threat to the fishery of Lake Mead and other reservoirs of the lower Colorado River (Miller 1952). The evidence now suggests that their value as a forage fish may override their predatory capabilities

(Crossman 1959a, 1959b; McAfee 1966). Further spread of this species should be watched with caution as both R. batteatto and R. egtegiws (Lahontan redside) intergenerically hybridize with a native cyprinid, the speckled dace

R. oscutto (Calhoun 1940, Weisel 1955).

Leatherside chub

The leatherside chub, Gi.ea cop&i, is a relatively small cyprinid

( <152 mm TL) native to the Bonneville Basin. It was found in bait shops from Lake Mead to Yuma, Arizona, and along the upper Colorado River drain- 162 age into Wyoming in the early 1950's (Miller 1952). This species has not been taken from Colorado River bait tanks in recent years and is yet to be recorded from open waters in the state (Minckley 1973).

Utah chub

The Utah chub, Gita atitania, is a native to the Bonneville System into the eastern edge of Nevada. Specimens have been taken above Lakes

Mead and Powell (Minckley 1973) and from bait shops below Hoover Dam

(Miller 1952, Jonez and Sumner 1954). This species is highly adaptable and quite prolific with the capabilities of degrading established sport fisheries (Carbine 1936, Davis 1940, John 1959, Olson 1959, Graham 1961,

Sigler and Miller 1963). Continued restrictions on bait dealers by Arizona and Nevada are necessary to prevent further expansion of this chub.

Mountain-sucker

AFS recognizes the mountain-sucker as Catostomm ptatrythyachus based on the synonymy of Smith (1966) that united the mountain-sucker, P.

Oatokynchuis, and the Lahontan sucker, P. Lahontan.

Arizona fishing regulations allow the mountain-sucker, Pantesteu4

OcayAhynchm, to be used as a bait fish in the waters of the Colorado

River common to the boundary between Arizona and Nevada. I have not found them in Arizona bait shops and their importance to the bait fish industry is minimal.

Utah sucker

A single yearling Utah sucker,Cato.stomm andms,was collected from a bait box on Lake Mead in February, 1951 (Jonez and Sumner 1954). This species presumably hybridizes with C. .Catipinnis in the Santa Clara River which eventually flows into Lake Mead but it is doubtful that either the sucker or the hybrid would find Lake Mead suitable. Utah suckers are of 163 no importance to the fishery other than the slight role they may play as a bait fish.

Longjaw mudsucker

There is an early record of longjaw mudsuckers, Gittichthy4 being sold as bait at the Lake Mead boat dock in 1950. The dealer indicated that they were flown in from Mexico, possibly from San Quintin in northwestern Baja California (Miller 1952). Gittichtho sp. is included in a partial list of bait fishes used in Lakes Mead and Mohave in the 1950's

(Jonez and Sumner 1954). They are occasionally used as cut fish bait in reservoirs in central Arizona (Minckley 1973) and Lake Mead, but do not present a serious threat to Arizona fisheries since they cannot reproduce in fresh water (Weisel 1948, Barlow and de Vlaming 1972).

Mottled sculpin

Sculpins are an unattractive group of bottom-feeding marine and freshwater fish that are common in eastern Nevada and western Utah. They may be established at least locally in Arizona (Minckley 1973). In 1949, 0. L. Wallis observed mottled sculpins, Cattws baikdi, in a bait tank at Lake Mead boat dock and obtained another from a bait dealer in Las Vegas

Wash. The origin of these fish might have been the Sevier River, Utah, where bait fishes are frequently seined (Miller 1952). Sculpins have been recorded below Davis Dam along the Colorado River and may be established, at least in small numbers, in the lower river in Arizona.

This species is potentially dangerous to Arizona fisheries since they prey on fish eggs and young fish; however, most data seems to indicate they seem to take their own eggs and young more commonly than other species

(Surber 1920, Koster 1937). Sculpins may serve as an important forage fish for lake and rainbow trout (Metzelarr 1928, Miller 1951, Rawson 1961) and do not necessarily deserve their notorious reputation (Zarbock 1951,

1952). 164

Brook trout

The brook trout, Savainco 6ontinatZs, was one of the most important sport fishes in the Southwest during the early 1900's. They have been replaced by the more popular rainbow trout in many of the high mountain streams and lakes where they once flourished. The brook trout was the first species stocked by the NPS in the Colorado River in the Grand Canyon in the 1920's. NPS records show 5,000 brook trout were released in Bright

Angel Creek (rivermile 88.7) in 1920 and 50,000 fish were released in

Clear Creek (rivermile 156.8) in 1927 (Wallis 1951). They were only occasionally reported from the river until 1977 when AGE reintroduced the trout above Lee's Ferry. A total of 200,000 brook trout were stocked into the Colorado River from 1977 to 1979. The brook trout is still rare in the river above Lake Mead but they are expected to become more common as the AGE stocking program continues.

Coho (silver) salmon

The first stocking of coho salmon, Oncokhyuchto Li!,utch, in Lake

Mead was in 1969 when AGED released 36,710 fish. Initially they exhibited an even greater growth rate than rainbow trout (AGED 1969) and produced a high return near the areas where they were released. Ripe males and females were observed in the summer of 1971 which gave evidence the original stock had matured in only two years instead of the normal three. The early maturation may have been attributed to an abundance of forage fish and the relocation of this species to a more southern latitude. AGED reported a stable population in 1973-1974 with salmon representing 2.3 percent of the total angler catch. The Nevada state record for coho salmon (4.0 kg) was taken from Lake Mead in 1974. The coho fishery began a rapid decline in 1975 and was eliminated by 1977. 165

In January, 1977, an angler reported a number of coho salmon at the back of Spring Cover in the upper Virgin Canyon. Supposedly the salmon were schooling with largemouth bass in the shallow water near the spring outflow. The back of the cove was examined several days later but salmon were not observed and the area was re-examined in April with the same results. All evidence suggests this species has apparently left the Lake

Mead fishery and there are no plans for coho reintroduction into Lake Mead at this time.

Cutthroat trout

Initial stocking of cutthroat trout, Samo ctakki, in Lake Mead occurred in 1972. Two plants were made; one from Heenan Lake, California,

(38,998 fish) and one from Strawberry Lake, Utah (19,650 fish). Cutthroats were not stocked in 1973 and 1974, but the stocking program was re-initiated in 1975 with the release of 7,732 fish. Cutthroat releases continued in

1976 (120,373 fish) and 1977 (148,426 fish). The first appearance of cutthroat in anglers' creels was in 1973 when an estimated 1,461 fish were taken from the lower lake (NFG 1973). The following year an estimated

4,655 fish were returned to the angler but their importance to the fishery was short-lived and by 1977 only 171 fish were caught. Cutthroat represented only 0.02 percent of the total angler effort in 1977 (NFG 1974, 1975,

1976, 1977) (Figure 8). Four cutthroat that were originally released near Saddle Island in Lake Mead were examined by a creel clerk at Lake

Mohave, which gives firm evidence that fish can successfully pass through

Hoover Dam.

Brown trout

A single brown trout, Sam tnutta, was taken by Paul E. Kitcha from

Las Vegas Wash on April 6, 1977. . Apparently the trout had been released in -0.6 total number harvested 6,000

percent total catch 0.5

5,000

Total number harvested . 0.4 2uao1aa

4,000 Tuqol

r 0.3 3,000 goqeo 0.2 2,000

0.1 1,000

I I I 1

Ni Figure 8. Estimates of total harvest and percent total catch of cutthroat trout from Lake Mead, Arizona-Nevada, 1972-1977. 167

the upper reaches of the Colorado River. The brown trout is rare to the

Colorado River in Arizona but is infrequently collected from the upper river in the Grand Canyon (C. 0. Minckley, pers. comm.). This species has been recently released into Lake Mead by the NDW (Cal Allen, NDW, pers. comm.).

Bowcutt trout

The bowcutt trout (a hybrid between a male rainbow trout, S. gaiAdneti, and a female cutthroat trout, S. actAki) was introduced into the reservoir by NDW in 1975 and was stocked again in 1977. The first release was in

Callville Bay (28,908 fish, averaging 15 cm TL) and the last release was in the Boulder Basin (61,610 fish). Several of these fish have been recovered by routine sampling but they are virtually absent from creel surveys

(NFG 1975, 1976, 1977). •

168

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